SUMMARY OF CURRENT RESEARCHES RELATING TO ZOOLOGY AND BOTANY (principally Invertebrata and Cryptogamia), MICROSCOPY, &c., INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS.* ZOOLOGY. A. GENERAL, including Embryology and Histology Influence of Gravity on Cell-division.t-Dr. E. Pflüger's experiments were conducted with the eggs of the frog. Each egg consists of a dark and a light hemisphere, and after fertilization the dark hemisphere always comes to lie uppermost, the "axis" of the egg being therefore vertical. When the black hemisphere is uppermost the line connecting its middle point with the middle point of the white hemisphere is termed the "primary axis"; to the primary axis correspond, of course, a primary equator and meridian. The "secondary axis" passes through the point at which the first and second planes of cleavage cut each other. The "tertiary axis" finally is any perpendicular diameter of the egg that is not coincident with either of the two former axes. The first two cleavages pass through the axis of the egg, and the third cuts it at a right angle; the question therefore arises, is there any real connection between the direction of cleavage and the axis of the egg, or do the first cleavages pass through the axis of the egg because it happens to coincide with the direction of gravity? By preventing the rotation of the eggs, by fixing them to a watch-glass in various positions after fertilization, Dr. Pflüger was able to show that the latter interpretation is the correct one; the first cleavages do not follow the axis of the egg but the direction of gravity passes along the vertical diameter, whether it happens to coincide with the axis or not. In the normal egg left to assume its own proper position with the dark hemisphere uppermost, it is well known that the process of division is far more energetic in the upper dark hemisphere, and this was believed to depend upon The Society are not to be considered responsible for the views of the authors of the papers referred to, nor for the manner in which those views may be expressed, the main object of this part of the Journal being to present a summary of the papers as actually published, so as to provide the Fellows with a guide to the additions made from time to time to the Library. Objections and corrections should therefore, for the most part, be addressed to the authors. (The Society are not intended to be denoted by the editorial "we.") + Pflüger's Arch. f. gesammt. Physiol., xxxi. (1883) pp. 311-8. some property special to this hemisphere. If, however, an egg be turned upside down during the process of division, it is found that the cleavage proceeds more vigorously in what is now the upper half and ceases to be so well marked in the lower half, and therefore clearly has nothing whatever to do with any special quality of different portions of the egg itself, but depends entirely upon its position. Another point to which Dr. Pflüger directed his researches was the relation that exists between the first cleavage and the axis of the future embryo; the experiments made appeared to show that the two are identical, and that each of the two cells therefore formed by the first division corresponds to one half of the body of the future embryo and also, a fact of the greatest importance, that the various parts of the body appeared to arise from the light or dark hemispheres according to the position of these latter; when the light hemisphere was uppermost the whole nervous invagination was seen to be clear and transparent. This part of the subject, however, the author does not consider to be as yet placed on a firm basis and intends to continue his investigations. * In a second paper on the same subject the author notes that among the tadpoles developed from the eggs some were remarkable by the dorsal surface being entirely free of pigment, owing to the fact that the light hemisphere had been fixed in the uppermost position; later, however, the pigment seemed to spread over the whole body, and no recognizable difference between the dorsal and ventral surfaces could be detected. The albinos also showed occasional abnormalities and soon died. A further investigation was made upon the eggs of Bombinator igneus; the main results appear to be the following: Quite normal embryos were developed when the upper hemisphere had a larger clear portion; but if it became almost entirely made up of the clear hemisphere the embryos were abnormal and died, though it was perfectly evident that the axis of the egg might be at any angle whatever with the direction of gravity, and not interfere in the least with the early developmental stages. In the earlier communication it was stated that the axis of the embryo coincided with the axis of the first cell-division, and that the central nervous system was formed out of the dark or the clear hemisphere, or out of both according to their position; a more careful investigation has shown that the central nervous system is always developed from the clear hemisphere. This fact appears to show that the egg is after all not "isotropous," and that a given organ arises from some particular region of the egg entirely independently of gravity; but another series of facts tends towards the opposite conclusion; in eggs fixed in an abnormal position the anus of Rusconi was never to be seen upon the upper hemisphere; again, when the primary axis was inclined at an angle the medullary groove was always developed with the anterior end in the upper portion and the posterior end in the lower portion of the white hemisphere, which latter, of course, was also obliquely *Pflüger's Arch. f. gesammt. Physiol., xxxii. (1883) pp. 1-79 (2 pls.). inclined to the horizontal. The position of the anus of Rusconi affords still further proof of a "relative isotropy"; it always appears upon the white hemisphere, and is intimately connected with the direction of the axes of the egg. The paper concludes with some observations on the development of Marsilia made by Dr. H. Leitgeb; it appears that in the embryo of this plant, the position of the first divisional septum in every case coincides with the axis of the archegonium; it is, however, capable of rotation round the latter, and as soon as the axis of the archegonium ceases to be vertical, takes such a position that the embryo is divided into an upper and lower half. The occurrence of the same principle of development in two such widely different types is evidently an indication of its wide-spread importance. Influence of Physico-Chemical Agencies upon the Development of the Tadpoles of Rana esculenta."-E. Yung subjected tadpoles just hatched to the action of saline solutions of various strengths. The salts employed were obtained by the evaporation of the water of the Mediterranean, and the larvæ were placed in solutions of 1, 3, 5, 7, and 9 per 1000, which were renewed at the same time in all the vessels, and the whole were in other respects placed under precisely the same conditions. As a general result, M. Yung states that the tadpoles are developed the more slowly the more considerable the degree of saltness of the water. In the solution of 9: 1000 no transformation took place, though some tadpoles live long enough to acquire hind limbs. In a solution of 10: 1000 very young tadpoles die in a few hours: elder ones survive for a few days. The author remarks upon the importance of placing equal numbers of individuals in each vessel in experiments of this kind, as their development is found to be slower in proportion to the number living together. M. Yung also subjected young tadpoles, which normally live in quiet water, to continuous agitation in a vessel containing two litres of water regularly renewed and suitable food. Under these conditions the eggs developed well; but the newly hatched tadpoles, being too feeble to seize their prey in so disturbed a medium, died of hunger, unless care was taken to give them daily a few moments of repose to take their food. If these tadpoles be compared, at different periods, with others of the same brood developing in quiet water, it is found that the developing of the former is slower, that they are less pigmented, which indicates bad nutrition, and, lastly, that their tails are relatively more developed, especially in width, which is explained by the greater use they are obliged to make of the organs in struggling against the waves. Colours of Feathers.t-The colours of the feathers of birds are of two kinds: (1) Objective, that is, colours caused by the presence of definite pigment, or by structural peculiarities of the feather itself, or * Arch: Sci. Phys. et Nat., x. (1883) p. 347. See Ann. and Mag. Nat. Hist., xiii. (1884) p. 72. † Proc. Zool. Soc. Lond., 1882, p. 409. finally by both causes combined; (2) Subjective colours are caused by the various effects of broken or reflected light. The colours owing to the presence of pigment are always black, brown, and red of various shades; only one instance is known of a green colour produced by pigment, and that is in the feathers of the Touracous. The violet and blue tints are never due to pigment alone, and often depend merely upon lines and grooves on the surface of the feather. There are numerous colours which appear to be due to the combination of definite pigmentary bodies within the substance of the feather, and the structure of the feather itself, and this is the case especially with blue feathers. If one of the blue feathers of a Macaw be pressed and broken so as to destroy its structure it appears to be of a brownish grey colour, which is owing to the presence of pigment of that colour. Dr. H. Gadow has published some interesting observations upon these colours. He finds that the blue feathers of many birds consist of an outer structureless sheath, beneath which is a layer of "cones" covered by a system of extremely fine lines running parallel with the long axis of the cone; below these cones lies a layer of brownish-yellow pigment, which appears black when present in great quantity. The whole surface coating of the feather varies not only in different birds, but in the different feathers of the same bird, and is in any case too thick to allow of the blue colour being explained in the way that other colours are produced by thin plates. The fine ridges upon the cones seem to be the source of the blue colour. The colours of yellow feathers are sometimes due simply to the presence of yellow pigment; but since many yellow feathers contain no pigment, this explanation will not hold in every case, In all probability a system of fine lines observed upon the outer surface of the feather is the cause. Similar lines occur in violet feathers, but they are finer and not quite so straight, and in this way, perhaps, the difference in colour is produced. With regard to the green colour of many feathers, the suggestion of Krukenberg, that it is caused by an admixture of yellow pigment and a blue optical structural colour, is not a sufficient explanation inasmuch as most green feathers do not show the same peculiar structures that are met with in blue feathers. All the green feathers examined show the following structure: a transparent smooth sheath covers the barbs and barbules; beneath this is a system of ridges and fine pits; the ridges are less regular than those of the yellow coloured feathers; beneath this layer is yellowish or brownish pigment. The second group of colours (subjective) are produced by a transparent sheath which acts as a prism. They are the so-called "metallic" colours, which change according to the position from which they are viewed. In describing the colours of birds a good deal of confusion has arisen from this fact, and Dr. Gadow suggests the desirability of introducing a standard method of describing these metallic colours in order to insure uniformity, and gives a diagram illustrating three positions in which the bird should be placed in order to describe its colours. Rudimentary Sight apart from eyes.*-Prof. V. Graber has instituted experiments to ascertain whether, and if so to what extent, eyeless and blinded animals are sensitive to light. As an example of the former he chose the earthworm; for the latter, Triton cristatus. The worms were placed in a box containing a number of cells of equal size, each with front and hind wall made of glass; the whole box was further divided into three parts, each of which had two front and two hind windows; the latter were turned from the light; and one of the windows of each cell was darkened, or supplied with a differently coloured light from that of the others. At the bottom of each was placed a layer of mud not sufficient to conceal earthworms. Twenty to thirty worms were first put into each cell and the box placed with one side towards a window with a north light. The number of worms found on the light and the dark sides respectively were counted at the end of every hour, and were replaced by fresh every four hours. Seven readings show that 40 specimens were found in the light, and 210 in the darkened spaces, giving a proportion of five of the latter to two of the former. Using opaque glass for one set of windows, 326 worms were found in the partitions thus relatively darkened, and 204 in the absolutely light ones. In employing light of different colours, care was taken that the one colour chosen should be very decidedly lighter than the other. As it soon became evident that red was more attractive to the worms than blue, a much darker shade of blue was chosen than that of the red; then in 12 divisions 193 specimens were found in the pale red light, and only 57 in the dark blue; this difference is the more remarkable as the worms, being naturally lovers of darkness, would, so far as intensity of light was concerned, have been expected to prefer the dark blue; it indicates an appreciation of the quality of the light. In like manner, white light, deprived of the ultra-violet rays, attracted 87, ordinary white light only 13 worms; of pale green and dark blue, the former colour attracted 138, the latter 42 individuals; of pale red and dark green, the former attracted 168, the latter only 72. In examination of a statement, that it is only the anterior end of the body which is sensitive to light, experiments were made upon worms deprived of this part to a length of four or five rings; they gave the proportion of worms found in the dark as 2.6 to 1 of those in the light, and that of those in red light as 2.8 to 1 of those in the blue-results tending in the same direction as those obtained from entire specimens. Applying the same method to newts, Graber found that while, of 160 uninjured specimens, only one was found in the light area, the rest being in the dark, 135 specimens from which the eyeballs together with a considerable length of the optic nerves had been removed, were found in the light, and 308 in the dark. The same result was obtained after the filling up of the eye-cavity by wax in some of the blinded animals, proving that the optic nerve had no action in producing this light-sensitiveness. Using coloured light, it was found that 192 * SB. K. Akad. Wiss. Wien, lxxxvii. (1883) p. 201. Cf. Naturforscher, xvi. (1883) pp. 437–9, and ‘Journ. of Science,' v. (1883) pp. 727–32. |