lOS 



GENERAL TRIXCirLES OF ZOOLOGY 



such animals are called separale-sexed, (//irr/(>//x or goiiorhorislir, in 

 opposition to the licniiapliroclilic forms, in which both kinds of sexual 

 glands are contained in one and the same indiviilual. Different degrees 

 of hermaphroditism can he distinguished; commonly testes and oxary 

 are contained in the same animal, some distance apart, as in the earth- 

 worm, in which two segments are male, while a third segment is female 

 (fig. 73). INIore rarely there is a union of testes and o\ary into a single 

 hermaphroditic gland; land-snails have an hermaphroditic gland, which 

 produces spermatozoa and eggs in the same follicle. 



Occurrence of Hermaphroditism. — Hermaphroditism is, in general, of 

 more frequent occurrence in the lower than in the higher animals. Insects and 

 vertebrates are, almost without exce[ilion, dia^cious; only among the telcosts is 

 hermaphrodilism not rare. It also occurs in the myxinoids. More commonly 



Fig. 74. — Lateral hermaiihrodilism of a gipsy moth [Oni-ria ilhpar). l.cft female, 

 right male i,aflcr Taschcnberg). 



hermaphroditism occurs as an abnormality; a striking form is lateral her- 

 maphroditism, in which one half of the animal has only male, llie other half only 

 female, gonads. If the males and females of a species be distinguishable by 

 their appearance, then lateral hermaphroditism is exjiressed in their external 

 form, since one half of the animal has the characteristic marks of the male, the 

 other half those of the female (tig. 7_j). Still it nnist be noted that, in many 

 instances where the external apjiearance poimed toward hermaphroditism 

 anatomical investigation has disclosed either onl\- male or onl\- female sexual 

 glands in a rudimentary condition (i^ynaiuIroiHorphisii.). 'I'rue hermaphrodilism 

 (the presence of both kinds of sexual glantls in the same animal) is extremely 

 rare in mammals and in man. What is described as hermaphrodilism is usually 

 gynandromorphism; rarely are both kinds of goiuuls present in the same indi- 

 vidual, and then not in a functional condition. 



The wide distribution of hermaphroditism among ihe lower Metazoa has 

 led to the erroneous view that this was the |irimili\e conilition, from which the 

 gonochoristic condition has been e\i>l\ed, Slttdies on nematodes, Crustacea and 

 possibly molluscs have shown that, on the conlrarv, hermaphroditism has fol- 

 lowed a dioecious condition, since with the disappearance of males, the female 

 animals may develop male sexual cells before the ovaries are mature. Con- 

 trasted to this ' prolainlry' a ' proloi^vinccv' is rare. 



Genital Ducts. — ^'ery frequently the excretory apparatus furnishes 

 outlets for the sexual products. In the annelids ami vertebrates portions 



