TRANSMIGRATIONS AND METAMORPHOSES. 235 



served for many years the purposes of study, have been 

 known to produce young ones as if they had been just 



laid. 



Natura non facit saltus is especially true as to the 

 division of sexes among the nematodes. Between the 

 true hermaphrodites and the true dioecious worms are 

 found species in which the males gi'adually dwindle and 

 become dependent on the female ; this is to be seen in 

 the Sphoerulari^, among which the male is only an 

 appendage to the female sex. We find here full evidence 

 of the fact that the female is more important than the 

 male, with regard to the preservation of the species. In 

 some species the sexes differ but little , in others, the 

 sexual differences become greater, and the male is only 

 one third of the length of the female ; but in some of 

 them the disproportion is greater still. At the same 

 time, we see nematodes whose males are attached to the 

 females, so as only to form a single individual ; in other 

 cases, the male seems to disappear to such an extent, 

 that we find nothing but the male organ in the female ; 

 indeed, there are instances of male worms, which, with- 

 out changing their form, occupy the cavity of the matrix 

 and, like the lernean crustaceans, are parasites of their 

 females. The Trichosomum crassicauda is an instance of 



this kind. 



Arrangements which would not have been suspected 

 beforehand, are every day revealed, with respect to the 

 conservation of species. We have recently learned from 

 the works of Messrs. Malmgren and Ehlers, and later 

 still, from those of Claparede, that in the same species 

 we may find different males, producing different off- 

 spring. Messrs. Malmgren and Ehlers have opened this 



