CRUSTACEA 285 



the sexes are distinct the males are very small and degenerate, 

 and live parasitically within the mantle -cavities of the 

 female. In Scalpellum omatum the males have no mouth ; 

 their appendages are rudimentary, and the body contains 

 little but the generative organs. In other species, e.g. 

 Scaljodlum vulgare, a similar male is found within the cavity 

 of an individual possessing female organs, but having testes 

 also. The male is called a complemental male, and it is 

 evident that the female has become hermaphrodite. Here, if 

 anywhere, ought to be found the opportunity of investigating 

 the origin of the hermaphroditism. This condition once 

 developed, the males tend to disappear from existence 

 altogether. This fact is in accordance with the principles 

 I am maintaining. Ova which develop without being 

 fertilised by the spermatozoa from a male can only develop 

 the acquired condition from a more or less distant male 

 ancestor. We do not know what determines the sex of the 

 offspring, but those which become males, as in other cases, 

 will develop the male structures, which in each generation 

 are usually confirmed by the influence of the conditions on 

 the individual. In the case supposed, self - fertilisation 

 occurring with the majority of eggs, this confirmation will 

 be wanting, and thus the inheritance of male characters will 

 become continually weaker. When the hermaphroditism is 

 so perfect that fertilisation by males . ceases altogether, 

 the eggs which develop into males will have nothing to 

 inherit, and only the eggs developing in the female direction 

 will give rise to the hermaphrodite adults, as in the majority 

 of Cirripedes. 



In the specially modified forms, Alcippe and Cryptophialus, 

 there is no hermaphroditism ; all are of separate sexes, and 

 the males are degenerate and parasitic upon the females. 



