The Larval Theory. xvii 



become encysted, are eaten, and grow within the sheep to 

 become adult sexual flukes. In this series the Cercaria 

 and fluke form members of the sexual division; all the 

 others are members of the asexual division of the cycle. 



In all cyclical propagation, whether in the animal or 

 vegetable kingdom, there is a tendency for one genera- 

 tion to become subordinated to the other. In flowering 

 plants the sexual is subordinated to the asexual, and 

 even some ferns exhibit a similar tendency, a fern- 

 plant rising vegetativel}'- from the prothallus ; while in 

 other ferns there is a tendency to apospory, a fern- 

 prothallus springs from the site of the spores, and the 

 asexual becomes subordinated to the sexual. In flukes, 

 in the same way, rediae may be budded off from the 

 sporocyst and the species be continued without ever 

 actually becoming sexual. In the Cynipidae it will be 

 seen that in some, like Cynips Kollari, the sexual genera- 

 tion has been wholly subordinated to the asexual, and 

 in others, like Rhodites rosae, this process is still going 

 on and males are becoming functionless and extinct. 



Leuckart^ regarded interpolated generations as larval 

 states, and following his teaching, Lichtenstein "^ looked 

 upon the agamous as larval stages of the sexual species. 

 He believed that the biological evolution of a gall-fly 

 extended from the time when a female emerged from 

 a true Gg^ in a condition to be fecundated by the male, 

 until another ^^g was reached presenting the same con- 

 ditions. All other stages he considered as larval, al- 

 though in them reproduction by budding was possible, 

 and he held that in this way insects might go on re- 

 producing themselves indefinitely without ever reaching 



^ R. Leuckart, Zur Kcnnf/n'ss d. Generationswechsels u.d. Parthenog. 

 b. d. Insekten, 1858. 



- J. Lichtenstein, Lcs Cynipides, 188 1, p. x. 



b 



