M. N. Pringslieim on the Pairing of Zoospores. 275 



two red spots. The four cilia, however, soon become motion- 

 less, and, together with the red spots, disappear. 



This act of conjugation occupies some minutes, i. e. from 

 the first contact of the zoospores to the formation of the green 

 globe. The latter becomes the oospore, which, after growing 

 slightly larger and assuming a red colour, germinates after a 

 long period of rest, and brings forth a new Pandorina. 



There is hardly any appreciable difference, except in size, 

 and that to no reliable extent, between the male and female 

 zoospores. Most frequently a small zoospore pairs with a 

 larger one ; but two of equal size (either of the larger or smaller 

 forms) often unite. Probably both the females and the males 

 vary much in size, the former more so than the latter. 



With regard to the entire plants from which the zoospores 

 are produced, there is little doubt that those of the largest size 

 are females ; but the sex of the smaller and middle-sized ones 

 cannot be determined with any certainty. 



The germination of the oospore is like that of other Volvo- 

 cinece, especially resembling in its early stage the germination 

 of the resting-spores produced by the microgonidia of Hydro- 

 dictyon utriculatum. The oospore bursts and produces a 

 single large zoospore (in rare cases two, or even three), which 

 divides into sixteen cells and becomes a young Pandorina. 



[The author then remarks that Cohn (in Volvox) and Carter 

 (in Volvox and Eudorina) describe the spermatozoids as differing 

 materially from the zoospores, and that they speak of the 

 brood-spheres as globular resting-cells. Whilst suggesting 

 some possible modes of reconciling the observations of Cohn 

 and Carter with his own on Pandorina^ the author admits that 

 further investigation of Volvox and Eudorina is necessary.] 



A comparison of the relations between the sexual act in 

 Pandorina Morum and that in other plants seems to afford a 

 clear insight into the gradual changes in the sexual products 

 and the sexual act in plants. 



Hitherto the conjugation of the Zygosporeoi has appeared to 

 have no affinity with the sexual act in other Algce ; and these 

 plants seemed, therefore, to form a sharply defined separate 

 group. 



Considering that in most plants the sexual organs differ 

 much in form and size, the doubts as to the copulation of the 

 Zoosjjorece seemed reasonable. The pairing of the zoospores 

 which takes place in Pandorina with hardly even an incipient 

 differentiation of the sexual organs, seems to be a fresh in- 

 stance of the act of copulation occurring in plants with motile 

 sexual organs, and it forms, therefore, a bridge between the 

 Zygosjwrea^ and the Zoospores ; and perhaps a more complete 



