52 THE CLASS OF INSECTS. 



"germ-ball" essentially agreeing with the ovnry, find the asex- 

 ual laryje 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 Aphides. Leuckart and Wagner farther agree, that " the 

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

 vitellus [yelk] remains without that envelope which has so re- 

 markable and peculiar a development in the 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, exacti3' as has been proved (by 

 Huxley) to be the case in the Aphides." .... "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 psedogenesis, which unites that of Miastor 

 with the parthenogenesis of the Coccidoi^ has been discovered 

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

 species of GJiironomiis laying eggs. But in the autumn other 

 pupre 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 Avonld 

 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 tlie forma- 

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

 cidm ; afterwards it resembles that of other Diptera {Simu- 

 lium and Chironomi dee ) , 



Dimorpiiism 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. Tims Cynips qxercvs-sjKivr/i^ficn occurs in male and female 

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



