GERM CELLS AND THEIR FORMATION 



105 



fertilization must be internal, and the sperm are then definitely intro- 

 duced into some reproductive cavity of the female. 



An interesting series of relations may be traced illustrating the grad- 

 ual increase in the certainty with which fertilization shall be accom- 



B 



E 



FIG. 53. Forms of spermatophores. A, B, C. The Insects, Loricera, Locusta, 

 and an Ichneumonid. From Korschelt and Heider, after Gilson. D, E. The 

 Urodeles, Amblystoma and Diemyctylus. From Bertram Smith. X 3. F. Peri- 

 patus edwardsii (incompletely developed). After von Kennel^CKorschelt and 

 Heider). 



plished, whether it be external or strictly internal. First, among many 

 of the Crustacea, Annulata, Gasteropods, Cephalopods, and Amphibia, 

 there is a process of pseudo-copulation or amplexus, where, sometimes 



