830 Proceedings of the Ohio State Academy of Science 



number of chromosomes but because the sporophyte happened 

 to acquire the habit of being nourished by the parent gametophyte 

 in its enibr}^onic condition. In some of the red algae where 

 both generations start as independent individuals the sexual and 

 nonsexual generations are practically alike in appearance and 

 complexity of structure. 



Wherever a sexual process is established a reduction division 

 must also occur in the life cycle. The reduction may take place 

 at three different stages. First, at the germination of the zygote; 

 second, just before the formation of the gametes ; or third, where 

 an antithetic alternation of generations is present, just before the 

 formation of the nonsexual spores on the sporophyte. 



In the evolution of sex, it was the gametes which were first 

 differentiated, both being produced on an hermaphrodite individ- 

 ual in nearly all the lower multicellular forms. As is well 

 known, a decided sexual dimorphism appears in the gametes and 

 often also in the sexual organs. The egg is large, stationary, 

 and with an abundant food supply. The sperm is comparatively 

 small, active and with a minimum of food stored in its body. 

 The first evolution or differentiation of sexuality is then an ex- 

 pression of difference in nutritive qualities. Xow what is the 

 hereditary apparatus that determines that the incipient gametes 

 shall develop as eggs in one part of the body and as sperms in 

 another part? As stated, the reduction in most of the lower 

 forms takes place at the germination of the egg spore. The 

 cause then which determines the development of gametes of one 

 kind or the other in the hermaphrodite body is a matter of the 

 becoming active or latent of characters common to all parts of 

 the organism. It is not at all the case that the sex of the gametes 

 is determined by the association or disassociation of an x or -a 

 2x number of chromosomes. It is a process similar in character 

 to that which determines that one leaf shall be a foliage leaf 

 and the one next to it a sporophyll ; or that one branch shall con- 

 tinue as a vegetative shoot and the other one develop as a fllower. 



