THE SPERMATOZOON 



141 



somewhat similar structure occurs in the toad. In some beetles there 

 is a fin-membrane attached to a stiff axial " supporting fibre " (Fig. 

 67, A). The membrane itself is here composed of four parallel fibres, 

 which differ entirely from the supporting fibre in staining-capacity 

 and in the fact that each of them may be further resolved into a 

 large number of more elementary fibrillae. 



Fig. 69. Unusual forms of spermatozoa. 



A. B. C. Living amoeboid spermatozoa of the crustacean Polyphemus. [ZACHARIAS.] 



D. E. Spermatozoa of crab, Dromia. F. Of Ethusa, G. of Alaja, H. of liiachus. [GROBBEN.] 



/. Spermatozoon of lobster, Homarus. [HERRICK.] 



J. Spermatozoon of crab, Porcellana. [GROBBEN.] 



Many interesting- details have necessarily been passed over in the foregoing 

 account. One of these is the occurrence, in some mammals, birds, Amphibia (frog), 

 and mollusks, of two kinds of spermatozoa in the same animal. In the birds and 

 Amphibia the spermatozoa are of two sizes, but of the same form, the larger being 

 known as "giant spermatozoa 11 (Fig. 67, G, //) In the gasteropod Paludina the 

 two kinds differ entirely in structure, the smaller form being of the usual type and 

 not unlike those of birds, while the larger, or "vermiform, 11 spermatozoa have a 

 worm-like shape and bear a tuft of cilia at one end, somewhat like the spermatozoids 

 of plants (Fig. 67, y, A'). In this case only the smaller spermatozoa are functional 

 (von Brunn). 



