6 FIRST GROUP. THALLOPHYTES. 



discovered by him in this plant. Pandorina (Fig. 16, I) is one of the commonest of the 

 Volvocineae. The sixteen cells of a coenobium are closely packed together in the thin 

 gelatinous envelope which surrounds them, and from which the long cilia project. 

 In the asexual multiplication each of the sixteen cells divides again into sixteen smaller 

 cells, which form themselves into a coenobium in the manner which will be described 

 further on in the case of Eudorina. The sixteen daughter-families (Fig. 16, //) are set 

 free by the solution of the gelatinous envelope of the mother-plant, and each of them, 

 invested with an envelope of its own, grows to the original size of the mother-family. 

 The sexual reproduction commences in the same way; but the gelatinous envelopes 

 of the young families become softened, and the individual cells thus liberated move about 

 freely by themselves (///) ; they vary very much in size, and are rounded and green at 

 the posterior extremity, narrow and hyaline and with a red corpuscle at the anterior 

 extremity, where are the two cilia. In the throng of swarm-cells pairs may be seen 

 approaching and as if they were seeking for one another ; these meet and come in 

 contact with their pointed extremities, and coalesce into a body which has at first the 



FIG. 17. Eudorina elegans. A coenobium in the act of forming daughter-coenobia, and with the gelatinous envelope of 

 the coenobium swollen. The cilia are only visible here and there, each cell of the coenobia having two. At c the cells are 

 still undivided, at b they are divided into two, at n into four ; ^i and a? are seen obliquely from above, a-i from the side ; 

 rf and e are more advanced stages of division ; in the state represented at c the daughter-coenobium is already a concave 

 disk and eventually becomes a hollow sphere by the folding over and union of its edges. 



shape of an hour-glass (IV] and by degrees contracts into a sphere (V], in which the 

 two red corpuscles and the four cilia at the enlarged hyaline end may be seen for a 

 short time only. The process of conjugation occupies a few minutes, and then the 

 zygospore is a spherical cell with a cell-wall ( VI\ which lies resting for some time and 

 changes its green colour to a brick-red. If the dried spores, which have in the mean- 

 time increased considerably in size, are put into water, they begin to germinate after 

 twenty-four hours ; the outer layer of the cell-wall bursts, an inner layer protrudes, and is 

 seen to contain two to three large swarm-cells ; these finally escape, and after swarming 

 for a short time become surrounded by a gelatinous envelope, and break up by repeated 

 divisions into sixteen primordial cells, which now again form a family like Fig. 16, /. 



