148 THE TESTES, BY V. LA VALETTE ST. GEORGE. 



The Frogs of this country, Rana esculenta and temporaries, 

 present this difference in the form of their spermatozoa, that in 

 the former the capitate extremity is thick and cylindrical, 

 whilst in the latter it is quite linear. 



REPTILIA. The spermatozoa of the scaly Reptiles have a 

 thickened cylindrical or fusiform head with a long tail Lacerta, 

 Coluber (Ecker). 



AVES. A similar form recurs in Birds. The head is either 

 simple, cylindrical, and straight, as in the Pigeon, Heron, Gull, 

 and the Rapacious and Climbing Birds, or it has acute edges, 

 and is twisted spirally. 



Fig. 179. 



Fig. 179. Spermatozoon of a Canary. 



MAMMALIA. The spermatozoa of Mammals are so far con- 

 structed upon a common type, that they all possess a thickened 

 capitate extremity approximating more or less to the form of 

 a disk and a thread-like appendage or tail. 



In the Pig the head is oval, with a recurved point, and is 

 equally flattened on the two sides. Those of the Bull, Sheep, 

 and Horse possess a similar form. 



Amongst the Rodentia, on the other hand, the shape is very- 

 various. 



In the Rabbit the capitate extremity is oval, flattened at 

 the sides, and truncated where it is attached to the thread-like 

 tail ; in the Guinea-pig it forms an almost circular disk, that 

 at the upper border likewise exhibits a peculiar caplike 

 appendage. 



Fig. 180. 



Fig. 180. Spermatozoon of the Mouse. 



Those of the Rat .and Mouse possess a hatchet-shaped 

 head, the tail forming as it were the handle of the hatchet. 

 The upper recurved extremity of the head is long and pointed 

 in the Rat, shorter in the Mouse, and sinuous in the Field-mouse. 



