The sections will then stand thus:

I. DISCIDA.-Mostly discoidal, sometimes elliptical, rarely cylindrical or spheroidal. Skeleton in part intracapsular, and consisting always of both circumferential and radial parts, which may be quite irregularly disposed, but which properly form an external, perforated shell, with an internal partition or spheroidal mass, forming a series of mutually communicating chambers, which are either concentrically or spirally arranged. No flagellum. Growth, multipolar or centrifugal. No nuclear vesicle.

II. FLAGELLIFERA.-With a flagellum. No nuclear vesicle. III. ENTOSPHÆRIDA. With an intracapsular spheroidal shell; not traversed by radii. No nuclear vesicle.

IV. ACANTHOMETRIDA. With radial skeleton, the radii of which meet in the centre of the capsule, and consisting more or less of acanthin. No nuclear vesicle. Yellow cells generally absent. V. POLYCYSTINA. Simple, ectolithic forms, with more or less compact skeletons, often with unipolar growth. No nuclear vesicle. VI. COLLOZOA.-Simple or compound. If single, then with the skeleton in the form of circumferential detached specula only. No nuclear vesicle.

VII. VESICULATA.-With a nuclear vesicle.

Oblique Light for Photo-micrography.-In a letter written by Dr. Woodward to M. Deby, the Vice-President of the Belgian Microscopical Society, in September last, he describes the method he makes use of when it is necessary in photo-micrography to use very oblique light, as in the case of Nobert's test, Amphipleura pellucida, &c. A pencil of parallel solar rays (reflected by the heliostat and plane mirror) is intercepted by the cell containing the solution of ammonio-sulphate of copper and a diaphragm which only allows the passage of a circular pencil of inch in diameter. The light enters parallel to the optic axis of the microscope placed horizontally and on the same level, but at a lateral distance (either right or left) of 3 inches. If the light is intercepted by a large achromatic prism of a focal length of about 3 inches, the desired obliquity can be obtained without difficulty. It is indispensable that the stage of the microscope should be very thin, or otherwise a false stage must be adopted like that supplied by Powell and Lealand. The best result is obtained when the rays are concentrated to a focus on the object itself. The illumination thus obtained is in general sufficient to produce negatives by the wet process up to 2500 diameters with three minutes' exposure.*

The Birth of a Rhizopod.-Professor Leidy has made some observations on this subject, which he records in the Proceedings of the Academy of Natural Sciences of Philadelphia':

I have long sought for the mode of multiplication of the testcovered Rhizopods, but thus far with little success. It appears as if the different forms with which we meet are always mature, and rarely are individuals seen with the ordinary characters which distinguish young from adult animals.

*Bulletin de la Société Belge de Microscopie,' vol. iv. p. 61.

Recently I observed a pair of conjoined individuals of Euglypha alveolata, which in their procedure appeared to coincide with the mode of multiplication of Chlamydophrys stercorea as described by Cienkowski. One of the Euglypha was one-seventh of a millimetre long (0.14 mm. long, 0.068 mm. in the short diameter), and had four long spines diverging from the fundus of the test. This was replete with the contents, including the usual large nucleus; and it presented no perceptible interval between the mass of sarcode and the interior surface of the test. The sarcode was mingled throughout with particles of food, and also included a large Navicula. The food was not collected in balls contained in vacuoles, but was diffused through the sarcode from the mouth to the fundus of the test, imparting to it a brownish hue. The globular nucleus measures of a millimetre.

Closely adherent to the mouth of the larger or parent Euglypha was the smaller or younger one, little more than half the size of the parent (measuring 0.08 mm. long and 0·06 mm. wide). The young Euglypha had the fundus somewhat abruptly narrowed and acute, and projecting from it the same number of spines as in the parent test. The peculiar structure of the test was apparent, but appeared less extended or unfolded. The contents filled the test, and consisted of clear, colourless, finely granular protoplasm, without any mixture of food, and without a nucleus.

Such was the appearance of the conjoined Euglypha parent and offspring at the commencement of the observation at 6 o'clock in the morning.

Closely watching the pair, the young Euglypha was noticed slowly to enlarge, and the brownish matter of the parent sarcode gently flowed into and became gradually diffused with the previously clear, colourless sarcode of the child. The fundus of the latter extended and became obtusely rounded, like that of the parent. The large nucleus of this disappeared or became so completely obscured as not to be visible. For some time there was no further very perceptible change within either test.

An hour from the commencement of the observation the young Euglypha had nearly acquired the size, shape, and appearance of the parent, and it measured 0·112 mm. long and 0.064 mm. broad. Now commenced an active circulation, a cyclosis, of the contents of the two tests, resulting in a thorough admixture. The sarcode flowed continuously from the parent on one side through the mouths into the child, and back again on the other side. Both tests were replete with one continuous mass of brown granular sarcode without nucleus or contractile vesicles, but with the Navicula which remained within the parent. During the circulation of the sarcode, two of the spines with the circular scale at their base became detached from the young Euglypha. The circulation ceased. At 7 o'clock I first observed the appearance of a contractile vesicle, 0.016 mm. in diameter, at the fundus of both animals. The vesicle collapsed and reappeared in two, three, or four, each again successively collapsing. With the appearance of the contracting vesicles the contiguous sarcode began

to clear up the brownish matter accumulating in advance of the usual position of the nucleus when present.

At this time the young Euglypha measured 0.116 mm. long and 0.064 mm. broad.

The sarcode of the parent now contracted at the middle, leaving a space between it and the test. The same change occurred in the child. The sarcode of the parent next cleared up in the vicinity of the mouth, then separated from that of the offspring, and retracted a short distance within the mouth.

At 5 minutes to 8 o'clock the two Euglypha bent slightly from side to side, protruded delicate pseudopods, and in two minutes afterwards were completely separated, with their mouths directed downward, and their fundi turned towards my eye.

Half an hour after separation a pale nucleus had made its appearance in both individuals, occupying the usual position, and measuring 0.028 mm. in diameter. Two or more contractile vesicles disappeared, and reappeared around the position of the nucleus. While the parent retained the original size, the young Euglypha was 0.12 mm. long by 0.064 mm. broad.

From this observation of the mode of multiplication of Euglypha, coupled with that of Cienkowski on the multiplication of Chlamydophrys, it may be inferred that all the test-bearing Rhizopods multiply in a similar manner.

The mode of multiplication of these Rhizopods reminds one of the mode of production by division of the Desmids, and in observing the process in the Euglypha I was forcibly struck with its resemblance to the mode of production of Arthrodesmus octocornis. The production of the young Rhizopod would correspond with that of a half cell of a Desmid.

Apparent Discriminative Power in the Selection of Food by a Heliozoon.-Professor Leidy also stated to the Academy that he had on several occasions observed actions in the Rhizopods apparently indicating a discriminative power in the selection of food. It was certain that they generally swallowed living Algæ and Animalculæ, and avoided dead ones. He recently had observed a Heliozoon eject an article which appeared to indicate a discriminative power. The Heliozoon was Acanthocystis spinifera. The genus differs from Actinophrys in being provided with siliceous rays in addition to the ordinary soft rays. The former emanate from minute disks, forming as it were a sort of flexible armour to the body of the Acanthocystis. While examining an individual, a rapidly moving oval flagellate Infusorium, as it was supposed to be, came into contact with several of the soft rays. The Infusorium was paralyzed; it assumed a globular shape and became quiescent. It was gradually drawn towards the body of the Heliozoon, which projected its armour to meet it, but quickly withdrew it again, and the Heliozoon was pushed off beyond the siliceous rays. The same movements were repeated, and then the Infusorium remained outside the siliceous rays. The objects were examined from time to time for several hours. The Infusorium was no more drawn towards the body of the Heliozoon. After a time it

projected a minute bud, which gradually extended into a tortuous tube, proving the supposed Infusorium to be a zoospore. It was finally abandoned by the Heliozoon, apparently as if it had been determined not to be its proper food.

On the Feeding of Dinamoeba.-These curious amoeboid animals take their food at what may be considered the posterior part of the body, and one instance, observed by Professor Leidy, appeared to him to be particularly interesting, and was related as follows:-Seeing a specimen of Dinamaba with its left side in contact with a filament of the Alga Bambusina Brebissonii, he was led to watch it. On closer examination it proved that the Alga entered to the left of the tail, and extended through the body, causing a slight bulge of the ectosarc by its other end to the left of the head. The Dinamaba became slightly elongated, and the Alga sunk more inwardly from behind. The former moved with an inclination to the right, causing the Alga to assume an oblique position from left to right. The anterior end of the Alga suddenly protruded from the body of the animal, so that this appeared to be pierced by it. In this condition the Alga entered the Dinamaba to the left of the tail and protruded at the right of the head. Gradually the Alga was made to assume a transverse position. The right extremity of the Alga now became depressed and the left elevated, so that the Alga assumed nearly its original position, in which it appeared to perforate the left border of the animal obliquely from the tail end. It gradually acquired a central position, penetrating the animal from tail to head. The Dinamoeba now elongated at both ends a third greater than its former length, extending in a fusiform manner upon the Alga. The animal next doubled upon itself, so that both ends of the Alga approached in front and protruded side by side from the head. One extremity of the Alga then sank within the Dinamaba, and subsequently the other extremity, so that the filament about three times the length of the animal became coiled up within it.

The observation of swallowing the Bambusina was made in the afternoon. In the evening, several hours after the first observation, on looking at the Dinamaba which had been preserved in an animalcula cage, it was observed sitting as it were on a large filament of the Alga Didymoprium Grevillii. The posterior end of the animal extended as a cylindrical expansion along the Alga to a greater length than the breadth of the body of the Dinamaba, and so closely clasped it as to contract the gelatinous envelope of the Alga to little more than the thickness of the green cells. After some time the Alga suddenly broke, and the two portions were gradually bent backwards, and made slowly to approach so as to become parallel with each other. One of the pieces was then drawn within the animal a convenient length, broken off and completely swallowed, and this was followed by a similar movement of the other piece. Shortly after the first rupture of the Alga, when the two portions projected at an obtuse angle from the back portion of the Dinamoeba, the animal contracted in length and discharged from the right side a mass of bodies which consisted

of the separated cells of Bambusina, probably from the filament it had swallowed in the afternoon.

These observations apparently explained certain facts in the habits of the animal. Dinamaba had been noticed to be especially fond of the Alga Didymoprium, for it was found to be present as the principal element of the food in numerous specimens. Bambusina was less frequently found among the food contents of the animal. The Alga were equally abundant in the localities of the Dinamaba, and from the observations detailed it would appear that the Didymoprium is preferred as food from the comparative ease with which its filaments are broken into pieces of convenient size for swallowing.

The observations are, moreover, interesting from their indicating discrimination and purpose in the movements of one of the simplest forms of animal life. The movements are to be viewed as reflex in character, though resembling the voluntary movements by which the most intelligent animal would prepare morsels of food of convenient form to take into the mouth. In striking contrast were the movements, noticed on several occasions, by which an Oscillatoria obtained entrance into the empty shell of an Arcella, and there, coiled up, crept round and round incessantly.

On the Measurement of the Dihedral Angles of Microscopic Crystals.M. Em. Bertrand has communicated the following to the French Academy:

The goniometer of Wollaston, more or less improved, is the only apparatus now employed for the exact measurement of the dihedral angles of crystals, and with this instrument in its present condition very small crystals can be measured. There is, however, a limit beyond which it becomes insufficient, and a crystal whose sides are for instance only the thirtieth of a millimetre cannot be measured by means of it. A method which would allow the dihedral angles of microscopic crystals to be measured, presents therefore some interest, for the crystals are generally purer the smaller they are.

For this I have endeavoured to make use of the microscope, but the difficulty which was at once presented was the orientation of the crystal to be measured. By means of the procedure explained below, this orientation becomes useless, and we are able by an indirect process to calculate the angle of the two faces of a crystal without it being necessary to orient it.

Take a cube and place a crystal in any position on one of the faces of it. Suppose one of the faces of the crystal to be prolonged to meet the face of the cube on which it is placed, the projection of this face of the crystal on the face of the cube will form with two of the edges of the cube two plane complementary angles. If we suppose this face of the crystal prolonged beyond the face of the cube on which it is placed, we shall obtain upon two other faces of the cube two projections, making respectively, with two edges of the cube, plane complementary angles, and the direction of the face of the crystal will be *This word may well be adopted into the English vocabulary. VOL. I.

R