Ch. I] 



FORMATION OF THE SEX-CELLS 



11 



The shape of the spermatozoon is very different in different 

 species of frogs. In some species the head of the spermatozoon 

 is drawn out into a fine point (Fig. 7, A, E) ; in other forms it 

 ends bluntly (Fig. 7, D). The middle piece is easily found in 

 some spermatozoa, but in others only by the application of 

 special reagents. In the European toad (Fig. 7, A) the tail of 



V 



M 



B 



/ 



Fig. 7. — Spermatozoa. A. Bufo cinereus. B-C. Two stages in development of sper- 

 matozoon; D. Fully formed spermatozoon of Hyla arborea. E. Spermatozoon 

 of Raua esculenta (the tail is too short). (After v. la Valette St. George.) 



the spermatozoon is formed by a flat membrane with a thick- 

 ened border. In Hyla arborea and Rana esculenta (Fig. 7, D, E) 

 the tail of the spermatozoon is like a long lash or thread. In 

 Rana esculenta the head measures .015-.021 mm. in length and 

 the tail .04 mm. in length. 



"Direct" Division of the Germ-cells 



In the testes of the frog and of other Amphibia are often 

 found germ-cells whose nuclei have very irregular outlines. 



