240 DEVELOPMENT AND EMBRYOLOGY. [Chap. XIV. 



ture males and females, propagating their kind in the 

 ordinary manner by eggs. 



It may be worth notice that when Wagner's remark- 

 able discovery was first announced, I was asked how 

 was it possible to account for the larvse of this fly hav- 

 ing acquired the power of asexual reproduction. As 

 long as the case remained unique no answer could be 

 given. But already Grimm has shown that another fly, 

 a Chironomus, reproduces itself in nearly the same man- 

 ner, and he believes that this occurs frequently in the 

 Order. It is the pupa, and not the larva, of the Chiro- 

 nomus which has this power; and Grimm further shows 

 that this case, to a certain extent, " unites that of the 

 Cecidomyia with the parthenogenesis of the Coccidae; " 

 — the term parthenogenesis implying that the mature 

 females of the CoccidEe are capable of producing fertile 

 eggs without the concourse of the males. Certain ani- 

 mals belonging to several classes are now known to have 

 the power of ordinary reproduction at an unusually 

 early age; and we have only to accelerate parthenoge- 

 netic production by gradual steps to an earlier and ear- 

 lier age, — Chironomus showing us an almost exactly in- 

 termediate stage, viz., that of the pupa — and we can 

 perhaps account for the marvellous case of the Cecido- 

 myia. 



It has already been stated that various parts in the 

 same individual which are exactly alike during an early 

 embryonic period, become widely different and serve 

 for widely different purposes in the adult state. So 

 again it has been shown that generally the embryos of 

 the most distinct species belonging to the same class 

 are closely similar, but become, when fully developed, 

 widely dissimilar. A better proof of this latter fact 



