CHAP. XXXVII.] DEVELOPMENT OF SPERMATOZOA. 



547 



The characters of the spermatozoa vary much in different animals ; thus 



in the rat and mouse the head or body is un- 

 symmetrical and curved. In the squirrel, the 

 anterior extremity of the head is rounded, 

 and wider than any other portion. In birds, 

 the head is usually attenuated. In reptiles 

 and fishes, the characters of the spermatozoa 

 vary much in different examples. Among 

 the invertebrata, those of the Crustacea are 

 very remarkable in form. For a detailed 

 account of the characters of the sperma- 

 tozoa in different classes of animals, we 

 must refer the reader to the excellent ar- 

 ticle, Semen, in the Cyclopaedia of Anatomy 

 and Physiology, by Wagner and Leuckart. 



Fig. 261. 



Spermatozoa of the river crawfish (as- 

 tacus fluviotilis). 



Fig. 2G'2. 



Development of the Spermatozoa. The development of the sper- 

 matozoa has been carefully investigated by Wagner, Siebold, and 

 Kolliker. The different stages are traced more readily in many 

 of the lower animals than in man. In the rabbit, Kolliker has 

 been able to observe the single spermatic filament within the cell 

 attached to the wall and making two or three turns in a spiral 

 form. It may now be looked upon as 

 almost certain, that each spermatozoon is 

 developed, not from any change of the cell, 

 but from the contents within the cell itself. 

 These cells are themselves developed in 

 the interior of a larger or mother cell, into 

 the interior of which the spermatozoa es- 

 cape by the rupture of their developing 

 cells, and are at last set free by the 

 destruction of the wall of the parent cell 

 itself. Professor Kolliker, in his latest 

 investigations, has arrived at the conclu- 

 sion that the spermatozoa are not developed 



'in flip rmolpi nf tllP pplta hut frnm fhpm "umber of spermatic filaments set 



us, out from mem. free from the nucki or cells of rievel _ 

 The nucleus becomes of an oval form, and P meilt - 

 one extremity is elongated to form the filamentary tail, while its 

 principal part constitutes the body of the filament. In this case, 

 they arrange themselves parallel to each other, the heads being in 

 one direction and the tails in the opposite. 



Movements of the /Spermatic Filaments. When the spermatozoa 

 have escaped, their active movements commence ; and by the con- 

 tinual vibrations of the filamentous tail, they are propelled forwards, 

 according: to Henle, at the rate of one inch in seven minutes and a 





