Journal of Microscopy,

AND

POPULAR SCIENCE.

NEW YORK, OCTOBER, 1878.

Volvox Globator.

BY ALFRED W. BENNETT, M. A., B SC., F. L.S.

No. 10.

for the first time followed out completely the various stages of reproduction of this singular organism. In no English work will they at present be found adequately described, although so many observers had before his time had it under their notice.

HE organism which The Volvox globator is not uncommon in we are about to de- clear pools on commons, and in similar scribe has long been situations, and is visible to the naked eye a favorite object as a minute pale-green globule rolling for observation to through the water, passing rapidly across microscopists, not the field of view under the microscope, its only from the ex- full diameter being perhaps one-fiftieth of traordinary beauty an inch. Under the microscope it is seen and delicacy of its that the rotatory motion is caused by instructure, but from numerable fine transparent vibratile cilia, the remarkable phe- with which the surface is studded. The nomenon which it appearance presented by the entire body is presents of a mem- that of a globular transparent, hollow member of the vegetable kingdom endowed with branous sac, through which these cilia proa power of motion apparently as spontane- trude, and studded with bright green ous as that possessed by any organisms be- points, while in the interior are seen a small longing to the animal kingdom. The very number of dense green globes. In the location of the Volvox among plants has in- autumn or early winter these internal deed been challenged. Like many others globes have often assumed an orange color, which are now placed, by almost universal giving to the whole globule a red tinge. consent, among the lower classes of Crypto- The vibratile cilia already described are gams, it was held by the distinguished nat- arranged in pairs, each pair belonging to a uralist, Ehrenberg, to be of animal nature. separate peripheral corpuscle or cell. These If, however, any doubt remained as to its peripheral cells contain each a green prototrue vegetable character, this has been com- plasm-body, varying in shape according to pletely set at rest by the researches of Pro- the age of the individual, as shown in Fig. fessor Cohn, who has only quite recently

*"Beiträge zur Biologie der Pflanzen," Vol. I, heft 3, 1875.

2, a, b; they usually contain a minute starch granule, a reddish-brown "eyespot," analogous to that of swarm cells

(zoospores) and of the Flagellate Infusoria, and carries on an independent existence

and one or two contractile vacuoles, the within the cavity of the mother colony, cilia being borne at the narrow hyaline end. each of its cells developing a pair of cilia; Each is surrounded by a gelatinous envel- finally it escapes from its confinement in ope, which is pierced by a number of canals, the mother colony into the surrounding all lying nearly in one plane, and filled by water. The normal number of parthenogreen or colorless extensions of the proto- gonidia which thus develop into colonies plasmic interior. Since the canals of ad- within the mother colony is eight, corresjoining cells correspond, the corpuscles ap- ponding to the eight cells into which each of pear as if connected together by a network them breaks up on its third segmentation. of fine reticulations. The outer gelatinous The young colonies complete their growth wall of each cell is also perforated by two in a few days, attaining a diameter of from pores, through which the two vibratile cilia 00.10 to 00.15 mm., and have by this time protrude into the surrounding water. They absorbed the greater part of the chlorophyl constitute a single peripheral layer envel- and starch of the mother colony. oping the entire organism, corresponding The sexual reproductive cells, male and to the plate which is characteristic of many female, are very few in proportion to the Chroococcaceae; each one by itself would be sterile cells. While the non-sexual reproundistinguishable from an ordinary swarm duction by parthenogonidia takes place durcell of many filamentous Algæ, or from the ing the whole year, the sexual cells are apentire individual of Chlamydococcus or Pleu-parently formed only in the autumn. The rococcus in its motile stage. They have, two kinds are found either in the same or however, so far as is known, no reproduc- in different colonies, establishing the classitive function, and in this respect stand fication of the genus into monoecious and almost alone among cells endowed with a dioecious sub-species, as first pointed out by spontaneous power of motion. Cohn. Fig. 1 represents a monœcious colBesides these non-reproductive or sterile ony. The two modes of reproduction do cells, there are in each Volvox colony three not take place simultaneously in the same kinds of reproductive cells-non-sexual colony, the sexual generation forming the (neuter), male, and female. The neuter close of a longer or shorter series of nonreproductive cells, or parthenogonidia, as sexual generations. Volvox presents, in Cohn terms them, are similar in structure fact, one of the earliest instances in the to the sterile cells, but two or three times ascending series of the phenomenon known their size, i. e. from .006 to .009 mm. in as alternation of generations, which attains diameter. Very early in the development its highest development in plants in the of the young colony they begin to multi- Vascular Cryptogams. The female cells ply by bipartition, and all the cells in the (gynogonidia of Cohn) are at first undissame colony or sphere are usually at one tinguishable from the parthenogonidia, but time in the same stage of development. are much more numerous. On their first This division has been followed by Cohn appearance they are about three times the through four stages, as shown in Fig. 3, size of the sterile cells; their protoplasm a-e, the fourth stage consisting of sixteen body increases rapidly, and becomes of a cells, beyond which he was unable to trace dark green color from abundance of chlorit, owing to the difficulty of the observa- ophyl. They have at first a frothy appeartion. At this stage it is described as hav- ance (Fig. 1, b) from the formation of vacuing somewhat the form of a blackberry, oles, but afterward appear to be filled with each segment possessing a single chlorophyl- protoplasm; and they are now at once disgranule containing starch. The young col- tinguishable from the parthenogonidia by ony is surrounded by a transparent mem- their never dividing. They soon become brane, which it at length breaks through, flask-shaped (Fig. 1, b2), their narrow end

varies greatly; Cohn has observed five or more male and about forty female cells.

touching the periphery of the sphere, and gelatinous envelopes (Fig. 1, b1, Fig. 7), the larger end hanging free into the cavity. and coalesce with their protoplasmic conWhen ready for impregnation they round tents or oospheres. The fertilized oosphere themselves off into a spherical form (Fig. is now an oospore, and develops a new 1, b3), and may then be designated cell wall, the epispore, which is at first oospheres, each being enveloped in a gela- smooth, but afterward covered with conical tinous membrane or oogonium. The male elevations, giving a section of it a stellate cells, or androgonidia, present at first a still appearance (Fig. 8). A second perfectly closer resemblance to the parthenogonidia, smooth membrane, the endospore, is subsesince, when they have attained about three quently formed within the first. The chlortimes the size of the sterile cells, they begin ophyl gradually disappears, and is replaced to divide; but they are of a lighter color, by an orange-red pigment dissolved in oil, from containing a smaller quantity of chlor- so that the mature oospore, while still inophyl. The divisions also take place only closed within the mother colony, is of a in two instead of in three directions, thus bright red color, giving the red tinge which developing, not into a sphere, but into a Volvox often presents, even to the naked plate of cells. They ultimately resolve eye, at certain periods of the year. Indithemselves into a bundle of naked primor- viduals containing oospores still enveloped dial cells (Fig. 1, a), each consisting of a in their spiny coatings were described by thicker but elongated body, in which the Ehrenberg as a distinct species, under the chlorophyl has been transformed into a red-name of V. stellatus. The number of sexual dish-yellow pigment, and of a long color- reproductive cells in a colony of Volvo.x less beak, to the base of which are attached two very long vibratile cilia, and where also is a red corpuscle or eye-spot (see Figs. 4, 5, 6). The whole androgonidium may now be considered as an antheridium inclosed in a gelatinous envelope, each of the naked protoplasmic bodies being a motile antherozoid or spermatozoid. About the same fall to the bottom and there hibernate. time that the gynogonidia have matured Their further development has only been into oogonia, and their protoplasmic con- observed by Cienkowski, who states that tents into oospheres, the movements of the the contents of each spore break up into vibratile cilia attached to the antherozoids eight spheres which ultimately swarm out. begin to set the whole antheridium in mo- Ehrenberg described two species of Voltion, in the positions indicated in Fig. 1, vox- -V. globator and V. stellatus-both of a, a2; the antheridium soon breaks up, and which he considered to be infusorial anithe separate antherozoids are seen in rapid malcules. These have been determined by independent motion within the gelatinous Cohn to be different stages of the same envelope of the antheridium (Fig. 1, a3), species, the former in its parthenogenetic, which they ultimately break through, and the latter in its sexually reproductive conthen move about rapidly in all directions dition; Ehrenberg's Sphærosira volvox is within the cavity of the mother colony. also another form of the same species. His Their movements are described by Cohn as Volvox aureus and Stein's V. minor are conbeing remarkably beautiful, the constant sidered by Cohn to form a distinct subcurvings of the elongated neck of the an- species of V. globator, differing from the therozoid being compared by him to those typical form in the colonies being of a of the neck of a swan. They assemble in smaller size, and dioecious instead of large numbers round the oogonia, and some monoecious, and in the epispore of the of them finally penetrate through their oospore being smooth. The mode of fer

Soon after the oospore reaches maturity, the mother colony breaks up, single cells escaping from the combination and swimming about freely in the water; their further history is unknown; while the oospores

tilization of the latter form has not yet been directly observed. The genus is cosmopolitan, having been found throughout Europe, in North Africa, India and North America.

A Few Remarks on Insect Dissection. Paper read before the Quekett Microscopical Club, Jan. 25, 1878, by T. Charters White, M. R. C. S., F. R. M. S., etc.

PERHAPS no field of microscopical re

The lengthening days of early spring already invite our attention to the resurrection of animal and vegetable life, and, like good generals, preparing for a campaign, we should begin to lay our plans for future work during the coming year. With the advent of our summer excur

The old family of Volvocineæ, which insearch teems with richer veins of included the genera Volvox, Eudorina, Pan- terest and instruction than that upon which dorina, Gonium and Stephanosphæra, is I have ventured to intrude this evening, placed by Sachs, in the Fourth edition of but feeling so deeply interested in it myself, his "Lehrbuch," under the Zygosporeæ, I may be pardoned if, in the absence of and in the section characterized by the con- others better qualified, I endeavor to throw jugation of zoogonidia (swarm-spores or out a few suggestions that will be of assistzoospores). It is evident, however, that the ance to those amongst us, who, taking up family, as so constituted, cannot be main- the scattered clews of my short paper, may tained, and Rostafinski's classification must work them into a fabric of surpassing be accepted as preferable, retaining those pleasure. genera which exhibit the conjugation of swarm-spores as a family of Zygospores, under the name of Pandorineæ, while the true Volvocineæ are placed in the class of Oosporeæ, in which the process of impregnation consists in the coalescence of one or more minute spontaneously motile antherozoids, which escape from an anther- sions many opportunities will be afforded idium, with a comparatively large oosphere us for leaving the busy throng, and excontained in an oogonium. The process indeed bears a very close analogy to the mode of fertilization in one of the highest families of Oosporeæ, the Fucaces. The family Volvocineæ, as thus constituted, includes at present only the two genera Volvox and Eudorina. The structure and developmental history of the latter have been described by Carter.†

EXPLANATION OF PLATE.

Fig. 1. A monoecious colony of Volvox globator, a, a2, a3, antheridia; b, b2, gynogonidia; b3, b4,

oospheres.

Fig. 2. Ciliated peripheral cells.

changing its bustle for a few short contacts with nature in her loveliest aspects; and while many of our members will find a revival of old delights in the capture of Conochilus and Volvox, there may be others who, like myself, see in their revolutions, beautiful as they are, only the same monotonous rolling as we have ever witnessed, and would rather behold something of that wondrous evolution manifested in the development of the various forms of insect life, so abundant in the early months of the year; and which may be compared to simple experiments in biological science, ready

Fig. 3. a-e, Parthenogonidia in successive stages made to the hands of the diligent students

of division.

Fig. 4. Complete antheridium.

Figs. 5 and 6. Antherozoids.

who will take the trouble to look for them. Of all anatomical studies, that which

Fig. 7. Oosphere containing antherozoids (see treats of the comparison of a particular also Fig. 1, b4).

Fig. 8. Fertilized oosphere.

All the figures highly magnified.

organ in one animal, with its homologue in another, yields the most untiring pleasure to those engaged in them. The study of comparative anatomy is inexhaustible in its

*This is the course followed in McNab's recent interest, and many amongst us would take

class-book of botanical classification.

"Annals of Natural History," Third Series, Vol. II, 1858, p. 237.

it up but for a mistaken notion which prevails, and leads many to suppose that all