140 Comparative Classification of Cynitidae 



and he came to the conclusion that they were glands 

 possessing a specific active secretion ; but it is undeniable 

 that when the intestine of a gall-fly is exposed, imme- 

 diately after it emerges from the gall, the function of these 

 rectal glands appears totally different. Indeed what 

 we find is, that the termination of the intestine is bulged 

 into a pouch by the liquid excreta ; and above that, just 

 where the rectal glands are situated, there is an annular 

 stricture, and consequently a closure of the intestine. 

 These glands therefore possess a mechanism analogous 

 to a sphincter ; now since they project into the intestine. 

 and are applied one against the other, whenever the 

 sphincter-like contraction takes place, an obstruction is 

 produced in the intestine, and the excreta cannot regur- 

 gitate into the anterior part. Although I have not 

 pursued narrowly the study of these prominences in 

 all the other orders of insects, I am able to state, from 

 the observations I have made, that they are especially 

 well developed in the case of insects which take liquid 

 sustenance, such as Hymenoptera, Diptera or Lepido- 

 ptera, and that they appear to be wholly wanting in the 

 Coleoptera. Accordingly I assume that these promi- 

 nences are only intended to aid in the closure of the 

 intestinal tube ; indeed without them it is difficult to see 

 how a re-fouling of the anterior part of the intestinal tube 

 could be avoided, in the case of those insects which ac- 

 cumulate liquid excreta at the lower end of the intestine. 

 The small amount of nourishment that the Cynipidae 

 take, indicates a brief existence as a perfect insect. 

 Life in both generations is short ; that of the winter 

 generation is a little longer than the other, some species 



