6 3 o SCIENCE PROGRESS 



in the life-history, there are certain forms (e.g. C. Kleinii) in 

 which this stage is much more prolonged and even dominant 

 (Schmidle 59). 



In its sexual reproduction Chlamydomonas shows many note- 

 worthy peculiarities. The majority of species are isogamous, 

 the gametes being formed by a similar process of subdivision of 

 the cell-contents as obtains in the case of asexual reproduction, 

 with the important difference that a larger number of divisions 

 occur (16 or 32 gametes are the rule) and that the products of 

 division ordinarily remain naked and conjugate in this condition. 

 A point of much importance, however, lies in the fact that in 

 those species of Chlamydomonas in which the first division-wall 

 is longitudinal the gametes are provided with an enveloping 

 cell-wall, which is cast off just prior to or during conjugation 

 (fig. 1, f). This is no doubt to be regarded as a primitive feature, 

 which coincides well with the probably primitive nature of 

 longitudinal divisions in these species. The only anisogamous 

 form is the well-known C. Braunii (Goroschankin 29) ; here 

 there is a constant difference in size between the (clothed) 

 gametes derived from different mother-cells, and conjugation 

 always takes place between a large gamete, which has come to 

 rest, and a much smaller motile one (fig. 1, g). The zygospores, 

 which are capable of passing through a prolonged resting-period, 

 are provided with a thick stratified membrane and generally 

 contain a quantity of red oil. On germination the oil is absorbed, 

 the contents become green, and subdivision of the latter takes 

 place, resulting in the formation of a number of ordinary 

 Chlamydomonas-individuals. In a few species (e.g. C. gigantea), 

 resting-stages are formed in a different way ; the contents of an 

 ordinary individual slip out from the cell-membrane and, after 

 performing metabolic movements for a little time, become 

 rounded off and excrete a thick membrane (constituting a 

 so-called cyst). 



Apart from the three very closely allied genera Chlamydo- 

 monas, Chloromonas (Wille 69), and Carteria, the Chlamydo- 

 monadaceae include a number of forms, which show more 

 considerable differences. It is unnecessary, however, to deal 

 with these in any detail, but one or two points of interest may 

 be indicated. The genera Chlorogonium and Hwmatococcus 

 (Wille 69, Wollenweber 71) are peculiar in having a considerable 

 number of contractile vacuoles (v) distributed through the proto- 



