THE CANADIAN ENTOMOLOGIST 127 



BOOK NOTICES 



A Contribution to the Morphology and Biology of Insect 

 Galls. By A. Cosens. (Reprinted from the Transactions of 

 the Canadian Institute, Vol. IX., pp. 297-387, 13 pis., 1912.) 

 That aspect of cecidology which treats of the causes that are 

 operative in the formation of insect galls and the manner in which 

 the plant tissues react to the stimulus is one that has been much 

 neglected, particularly by American students of the subject. Mr. 

 Cosens' work throws considerable light on these interesting prob- 

 lems and is one of the most important contributions to our 

 knowledge of the morphology of galls that has ever been published. 



The greater part of the work is devoted to descriptions of the 

 anatomy of sixty-eight kinds of American insect and phytoptid 

 galls. The descriptions are arranged in the order in which the 

 producers are classified, most of the gall-producing families, ex- 

 cept those of the Coleoptera, being represented. 



Although dealing mainly with matters that are chiefly of 

 interest to the botanist, the author has also cleared up some im- 

 portant difficulties concerning the feeding habits of various gall- 

 producing insects. Cynipid larvae were found to secrete an enzyme 

 which converts the starch in the nutritive layer of cells surround- 

 ing the larval chamber into sugar, which is taken up by the larva 

 through the mouth. The cells of the larrval chamber thus remain 

 unbroken, and their inner surfaces present a marked contrast to 

 the ragged cell-layer lining the cavities inhabited by inquiline 

 larvse. This view is confirmed by the discovery that though, 

 contrary to current views, the intestinal tract in Cynipid larvae 

 is complete, an anus being present, no frass is expelled, as would 

 be the case were the entire cells devoured, as they are in sawfly 

 galls. 



It is suggested that this ferment "may indirectly stimulate cell 

 proliferation by storing the nutritive zone with an unusually large 

 quantity of available nourishment, which can diffuse to all parts 

 of the gall." 



Adler's discovery that the gall of Nematus vallisnierii is partly 

 formed while the larva is still within the egg, was confirmed in 



