MALE ORGANS OF GENERATION. 



557 



spending parts of an animal, but simply for the sake of conveni- 

 ence ; just as one might speak of the head of an arrow, or the tail 

 of a comet. 



In the lower animals, the spermatozoa have usually the same 

 general form as in the human subject; that is, they are slender 

 filamentous bodies, with the anterior extremity more or less en- 

 larged. In the rabbit they have a head which is roundish and 

 flattened in shape, somewhat resembling the globules of the blood. 

 In the rat (Fig. 184, b) they are much larger than in man, measur- 

 ing nearly T A 5 of an inch in length. The head is conical in shape, 



Fig. 184. 



SPERMATOZOA. o. Human. 5. Of Rat. e. Of Menobranchus. Magnified 4SO times. 



about one-twentieth the whole length of the filament, and often 

 slightly curved at its anterior extremity. In the frog and in rep- 

 tiles generally, the spermatozoa are longer than in quadrupeds. 

 In the Menobranchus. or great American water-lizard, they are of 

 very unusual size (Fig. 184, c), measuring not less than ? ' ? of an 

 inch in length, about one-third of which is occupied by the head, 

 or enlarged portion of the filament. 



The most remarkable peculiarity of the spermatozoa is their 



