CONJUGATION OF ZYGNEMA. 



335 



Lag down of the intervening partitions, so as to establish a free 

 passage between the cavities of the conjugating cells. In some 

 genera of this family (such as Mesocarpus), the conjugating cells 

 pour their endochromes into a dilatation of the passage that has 

 been established between them ; and it is there that they commingle 

 so as to form the Oo-spore. But in the Zygnema (Fig. loo), which 



Fig. 155. 



: ^L^^R0M^ 



Various stages of the history of Zygnema quininum: — a, 

 three cells, a, b, c, of a young filament, of which b is under- 

 going subdivision ; b, two filaments in the first stage of con- 

 jugation, showing the spiral disposition of their endochromes, 

 and the protuberances from the conjugating cells ; c, comple- 

 tion of the act of conjugation, the endochromes of the cells 

 of the filament a having entirely passed-over to those of fila- 

 ment b, in which the Oo-spores are formed. 



is among the commonest and best-known forms of Conjugate®, the 

 endochrome of oue cell passes over entirely into the cavity of the 

 other ; and it is within the latter that the Spore is formed (c), the 

 two endochromes coalescing into a simple mass, around which a 

 firm envelope gradually makes its appearance. Further, it may be 

 generally observed that all the cells of one filament thus empty 

 themselves, whilst all the cells of the other filament become the 

 recipients ; here, therefore, we seem to have a foreshadowing of the 

 Sexual distinction of the Grecerative cells into ' Sperm-cells ' and 

 'Germ-cells,' which we have just seen to exist in the Confervaceas. 

 And this transition will be still more complete if (as Itzigsohn has 

 affirmed) the endochrome of certain filaments of Spirogyra breaks 

 up before conjugation into little spherical aggregations, which are 

 gradually converted into nearly colourless spiral filaments, having 



