ONTOGENESIS 169 



another " species." One type is parthenogenetic, 

 the other sexual, in regular seasonal alternation. 

 Of some species, the male is unknown, and it may be 

 that the female reproduces continuously by partheno- 

 genesis. Development by zygosis seems to be only 

 an occasional incident to the life history of such a race. 



Artificial Parthenogenesis. Although not many 

 kinds of animals naturally develop agamically, yet 

 those that do are by no means " lower types." 

 On the contrary they are usually highly specialized, 

 and the ability to develop in this way is an expression 

 of their specialization. Such examples demonstrate 

 that whatever may be the function of the sperm in 

 zygosis, the egg of each species contains within 

 itself alone the potentiality of developing into an 

 individual, typical of the species of which it is a 

 member. Such being the case, if development can 

 be inaugurated in an egg that never normally develops 

 by zygosis, by analyzing the agency that brings 

 about such an effect, we may get a clue to the nature 

 of the action of the sperm in producing the same 

 result. Within the last few years a great deal of 

 experimental work has been done, which, although 

 perhaps it does not get very far in analyzing the 

 phenomena, does serve to show the subtle complexity 

 of the forces involved, and indicates the nature of the 

 stimulus exerted. 



Ij: was found first that potassium chloride added to 

 sea water in which were the matured eggs of a sea- 

 worm, Chcetopterus, induced the egg to undergo a 



