298 Transactions of the Canadian Institute [vol. ix 



investigators that in reality the host does derive benefit from the ab- 

 normal swelling since it has been the means of restricting the ravages of 

 the parasite to a limited area. 



I have confined the subject-matter of this research to the Zoocecidia 

 including the Insecta and Arachnida. In the Insecta the following orders 

 are dealt with — Hjmiptera, Lepidoptera, Diptera and Hymenoptera. 

 No attempt has been made to treat any one order exhaustively, but the 

 work was restricted to the living gall material at hand. As a preliminary 

 to the botanical work, several seasons were spent in rearing the producers 

 in order that unquestioned identification could be assured of the various 

 forms studied. 



Concerning the anatomy of our American galls, the only work done 

 previous to this is that by Cook,^^ who must be considered the pioneer 

 in this branch of the subject. The anatomical studies pursued are con- 

 sidered important as forming a foundation for deductions. 



The recent investigations of Weidel** on the early developmental 

 stages of Neuroterus have added valuable data to the ontogenetic work. 

 It is exceedingly necessary that some of the American species should be 

 worked out in the same manner, but before this can be done with assurance 

 of success, an American Adler must settle the questions concerning the 

 alternate generations of our native forms. 



Special attention has been paid to the Sawfly and Lepidopterous 

 galls, since the anatomy of the former has hitherto not been dealt 

 with at all and the ontogeny only very inadequately. The latter have 

 also been neglected to nearly the same extent. The order Diptera and 

 the family Cynipidae have presented the most interesting biological 

 phenomena, notably concerning the feeding habits and the nature of the 

 gall-producing stimulus, two factors that are closely parallel if not in- 

 deed identical in these two sections of the gall producers. 



With the exception of Pachypsylla celtidis-mamma Riley all the 

 material was collected in the vicinity of Toronto. It was fixed in picro- 

 sublimate or Flemming's weaker fluid and cut in series in paraffin or 

 celloidin. A double stain of safranin and haematoxylin was invariably 

 used. 



The investigations described in this paper were carried on in the 

 Botanical Laboratories of the University of Toronto under the super- 

 vision of Prof. J. H. FauU, who suggested the subject and to whom I 

 wish to acknowledge my indebtedness for invaluable criticism and as- 

 sistance throughout. To Dr. C. D. Howe I wish to express my obli- 

 gations for direction in the physiological experiments. My thanks are 

 also due to Mr. W. A. McCubbin, M.A., for valuable assistance in the 

 photography and to Mr. J. H. White, M.A., for normal material. 



