52 THE CLASS OF INSECTS. 



•'germ-ball" essentially agreeing with the ovary, and the asex- 

 ual larvae begin life as egg-like bodies developed from this 

 germ-ball, just as eggs are developed in the little tubes of 

 which the ovary is an aggregation. Hence these worms bad 

 out from the germ-stock, just as we have seen in the case of 

 the Apliides. Leuckart and Wagner farther agree, that " the 

 so-called chorion never being formed in either of them, the 

 vitellus [3'elk] remains without that envelope which has so re- 

 markable and peculiar a development in tlie true egg of in- 

 sects." .... ''The processes of embryo-formation agree in 

 all essential points with the ordinary phenomena of devel- 

 opment in a fecundated egg, exactly as has been proved (by 

 Huxley) to be the case in the AphidesJ" .... "The only 

 difference consists in the germ-chambers of the Cecidomyide 

 larviB separating from the germ-stock, and moving about freely 

 in the cavity of the body, whilst in the Aphides they remain 

 permanently attached, and constitute an apparatus which, in 

 its form and arrangement, reproduces the conditions of the 

 female organs." 



Another case of pgedogenesis^ which unites that of Miastor 

 with the parthenogenesis of the Coccidcn, has been discovered 

 by Grimm who found, in the spring of 1869, the pupa of a 

 species of Chironomus laying eggs. But in the autumn other 

 pupoe become flies without laying eggs, while the fly itself de- 

 posits a larger number of eggs than the spring pupa. Grimm 

 also found that on removing from the perfectly developed in- 

 sect, before it has left the pupa-case, the eggs which would 

 otherwise have been fertilized, and preserving them in water, 

 the development of the larva took place in them also, but 

 lasted a little longer (about six days). Previous to the forma- 

 tion of the primitive band, the germ develops as in the Coc- 

 cidce ; afterwards it resembles that of other Diptera {^Simu- 

 I him and C h i r o « o m i dm ) . 



Dimoi-phism is intimately connected with agamic reproduc- 

 tion. Thus the asexual Aphis, and the perfect female, may be 

 called dimorphic forms. Or the perfect female may assume 

 two forms, so much so as to be mistaken for two distinct spe- 

 cies. Thus Cynips quercns-spGngiJica occurs in male and female 

 broods in the spring, while the fall brood of females were 



