THE BREEDING HABITS OF ANIMALS 



191 



in other fishes and in the amphibians; and that it occurs as an abnormal 

 condition in reptiles, birds and mammals. In most of the cases of 

 hermaphroditism in the higher animals the individuals do not, however, 

 function as both sexes. They may be so abnormal as not to function 

 as either sex. "Concerning such forms, of course, there can be no discus- 

 sion of methods of insuring fertilization. 



Fig. 145. — Genital organs of a hermaphrodite animal, a common land snail Polygyra 

 albolabrls (Say). Note that some of the organs are characteristic of a male, others of a 

 female. 1, atrium; 2, penis; 3, prepuce; 4, vagina; 5, spermatheca; 6, vas deferens; 7, free 

 oviduct; 8, uterus; 9, spermatic duct; 10, talon; 11, hermaphroditic duct; 12, hermaphroditic 

 gland; 13, penis retractor; 14, albumen gland- 

 Only a few of the hermaphroditic animals, for example some nematode 

 worms and the parasite Sacculina, are self-fertilizing. In self-fertilizing 

 forms the eggs are usually fertilized within the body and there is no act 

 of copulation. In hermaphrodites that are not self-fertilizing the eggs 

 are in some cases fertilized within, in other cases outside of the body, 

 and various methods of insuring fertilization are to be observed. In 

 hermaphroditic hydras the spermatozoa are shed into the water and 

 find the ova, still within the body, largely by chance, perhaps assisted 

 by chemical attraction. In the earthworm, on the contrary, there is an 



