62 COCCOPHYCE.E. 



ruptured sphere, and seems to show that there is a denser layer of 

 thick matter, whatever its nature may be, disposed in a somewhat 

 regular manner, being concentrated near the south pole of the axis of 

 rotation, whence it spreads over the inner surface in streaks resembling 

 the lines of longitude on a terrestrial globe. 



" Both from its position and from the rapidity with which it is stained 

 by aniline purple, without which its existence is apparently absolutely 

 undemonstrable (in which respect it is in marked contrast to the outer 

 cell-wall, which latter is only faintly tinted by somewhat prolonged 

 application of the reagent, and then only where the hexagonal structure 

 exists) I have no doubt that this inner layer is the true ' primordia 

 utricle ' of the cell, and possesses that character of vital and formative 

 matter which distinguishes this element of cell-structure from the outer 

 wall, which, on the other hand, probably consists of cellulose or some 

 similar compound. Probably the arrangement of this inner layer, in 

 radiating lines or ribs, contributes to the elasticity of the fabric, whereby 

 it is enabled to open at a given point for the escape of the young, and 

 to contract again after their emission. 



" The increase of individuals by the means already described is 

 strictly an instance of subdivision. 



" But Volvox globator also affords an instance of true alternation of 

 generations. As may probably be affirmed of all living organisms, its 

 life-history would be incomplete without a process of sexual reproduc- 

 tion, and accordingly, after a long sequence of asexual generations, a 

 strictly sexual process intervenes, from which result certain spores 

 destined to lie dormant for a while, and, like the zygospores of the 

 Conjugate Algae, to resist vicissitudes of condition and climate 

 through the rigours of winter, and then to produce the parent form in 

 the succeeding year, when external conditions again favour its develop- 

 ment. 



" Cohn fully traced the various stages of this process, and desci'ibed 

 them in the ' Beitrage zur Biologie der Pflanzen ' (1875, Vol. I., Heft. 3), 

 and in the ' Annales des Sciences Naturelles ' (4 ieme Ser. Bot., Tom. 

 V., 323) ; and his observations have been more or less confirmed by 

 other investigators, especially by Carter (Ann. Nat. Hist., 3rd Ser., Vol. 

 III., 1859, p. 1), and more recently, in 1877, by a French botanist, M. 

 F. Henneguay. 



" Cohn and Carter both hold that there are two varieties of Volvox,* 

 one monoecious, the other dioecious, and the latter maintains that 

 Sphcerosira Volvox is the male form of the dioecious sub-species. Be 

 that as it may, the reproductive process in the monoecious form is as 

 follows : The sexual reproductive cells, male and female, occur in 

 spheres of unusual size in the autumn, and are few in proportion to the 

 number of sterile cells, and the reproductive process does not occur 

 simultaneously with, but as a climax to a long series of asexual genera- 

 tions. On their first appearance the gynogonidia or female cells are 

 about three times the size of the sterile ones, of a deep green colour, 

 and of a frothy consistency from abundance of vacuoles. They are 

 easily distinguished from the parthenogonidia by their never sub- 

 dividing. (Plate 22, Fig. 5b.) They next become flask-shaped, their 

 narrow end touching the periphery of the sphere, and the broader end 

 hanging free in the internal cavity. (Plate 22, Fig. 5# 2 .) Finally, they 

 assume a sphaerical form, and become oospheres, each enveloped in a 

 gelatinous membrane. (Plate 22, Fig. 5b 3 , & 4 .) 



" The androgonidia. or male cells, at first closely resemble the par- 

 thenogonidia, but undergoing division in two instead of three directions, 



* The two forms are here accepted, after Stein, as Volvox globator and Volvos 

 minor. 



