ZYGOSPORES. 



^55 



disappear. Some minutes after the commencement of conjugation the resulting 

 zygospore is a spherical cell {VI), which remains at rest for some time enclosed in 

 its cell-wall, its green colour passing over into a brick-red. If the dried-up zygospores, 

 which have now greatly increased in size, are placed in water, germination begins 

 after twenty-four hours ; the outer shell of the cell-wall breaks up, an inner membrane 

 protrudes and now contains one, two, or three large zoospores which finally escape 

 {Fill, IX), surround themselves, after a short period of swarming, with a gelatinous 

 envelope, and break up by successive divisions into sixteen primordial cells which 

 now again form a ccenobium like Fig. i. 



A further illustration of the course of development in the Pandorineae is furnished 

 hy StephanosphoBra plwvialis, one of the rarest and most beautiful of the family (Fig. i68), 

 occurring rarely in the rain-water which collects in the hollow of large stones. 

 The process of vegetative reproduction is the same as in Pandorina; but, according 

 to Cohn and Wichura, the succession of generations of this kind is interrupted by 

 the cells belonging to a family dividing repeatedly (Fig. i68, XII) into zoogonidia 

 which ultimately become free {XIII), and probably produce resting zygospores by 



Fig. i68.— Successive stages in the reproduction oi Stepkanosphara plumalis (after Cohn and Wichura). 



conjugation after the manner of Pandorina. It is stated by the observers above-named 

 ithat stationary immotile balls (/) accumulate at the bottom of the water which, as they 

 [grow, assume a red colour. After these resting-cells, which are probably zygospores, 

 [have lain for some time dry and then again been moistened, they germinate, the contents 

 )reaking up into from 4 to 8 zoospores {II— V) which invest themselves with a cell- 

 rail, and each gives rise, in a single day by successive division {VII— IX), to an 

 [eight-cell coenobium {X, XI), which again in the next night gives birth to eight 

 finotile families \ 



2. The nearest allies to the Pandorineae are probably the Hydrodictye^, as is 

 [shown by their formation of coenobia, and still more by the whole course of their de- 

 [velopment, which Pringsheim^ first described in detail. Although the conjugation of 

 the zoogonidia has in this case also not been actually observed, they offer a striking 



* [Archer has described, /. c, pp. 7, 8, a remarkable amoeboid phase which the primordial cells 

 \Siephanosphcera undergo.] 



* Pringsheim, Mon. der konigl. Akad. der Wiss. zu Berlin. Dec. 13, i860. [Ann, des Sc. 

 It. i860, vol. XIV; Quart. Journ. MIcr. Sc. 1S62, pp. 54, 104. See also A. Braun, Verjungung, 



46 ; Ray Soc. Bot. and Physiol. Mem. 1853, pp. 137, 190, see ante, p. 251.] 



