178 



BIOLOGY: GENERAL AND MEDICAL 



peculiar development of the phenomenon of conjuga- 

 tion by which in a certain sense the cell substance con- 

 joins with itself. 



Another curious form of conjugation is seen in Spiro- 

 gyra, where two cells side by side in the same filament 

 conjugate by the development of coalescing processes 

 which are formed near their transverse wall. Here 



FIG. 76. Mucor mucedo. Different stages in the formation and germination 

 of the zygospore: 1, Two conjugating branches in contact; 2, septation of the 

 conjugating cells (a) from the suspensors (&); 3, more advanced stage in the 

 development of the conjugating cells (a); 4, ripe zygospore (b) between the 

 suspensors (a) ; 5, germinating zygospore with a germ- tube bearing a sporangium. 

 (After Brefeld.) 



again there can be no doubt but that the conjoining 

 cells are the descendants of the same parent and so 

 closely related as to make the advantage of the inter- 

 change of substance of problematical value. 



From such indistinct differentiation of male and 

 female substance, and from aberrant forms in which, 

 as in Ulothrix, the gametes may either conjugate or 



