CONJUGAT.E 



271 



jugating protrusions disappears. The two protoplasmic bodies then 

 unite in the conjugating tube thus formed into a nearly spherical zygo- 

 sper?fi, enclosed in a cell-wall which ultimately becomes differentiated 

 into three layers, the innermost and outermost of which are colourless, 

 while the middle one is firmer and brown. The outer surface remains 

 in some species smooth, while in many it becomes, w'hen mature, 

 covered with warts or spines, which are not unfrequently barbed. In 

 those genera where the individuals are associated into filaments, conju- 



D 



Fig. 241. — Zygosperms of desmids. a, Euastrum pectinaUnn Brdb. (x 400). b, Penhim 

 inargaf-itacejun Brdb. (x 300). c. Closteruim rostratmn Ehrb. early stage (x 200). d, 

 Dt'SfnidiuKt Swartzii Ralfs ( x 600). (All after Ralfs.) 



gation takes place betw-een the cells of different filaments, and a 

 large number of zygosperms may frequently be seen in the same fila- 

 ment. In Gonatozygon (de By.), where the cells are very long and 

 slender, the process is very similar to that in Zygnema. The state- 

 ment of the occurrence of zoospores in the Desmidiaceae is founded on 

 erroneous observation, the antherozoids of parasitic fungi having pos- 

 sibly been mistaken for zoospores. 



After remaining for a considerable time at rest, the zygosperm ger- 

 minates by the bursting of its two outer coats, the protoplasmic contents 

 escaping still enveloped in the very thin innermost coat. In this embryo. 



