286 The Ohio Journal of Science [Vol. XVI, No. 7, 



Summary. 



1. There are seventeen known species of zoocecidia occur- 

 ring on Celtis occidentalis, belonging to four orders of arthro- 

 pods: Acarinae 1, Lepidoptera 1, Hemiptera 5, Diptera 10. 

 All are heteroplasias, i. e., those forms of hyperplasias (abnormal 

 increase in size through cell proliferation) whose cells and 

 tissues differ from the normal. All, be it noted, are built up on 

 the basis of the same germ plasm, viz., that of the single species 

 of the plant mentioned. 



2. The acarinous and lepidopterous galls are kataplasmas, 

 or those forms of heteroplasias whose cells and tissues do not 

 vary widely from the normal. Each shows specific and char- 

 acteristic inhibition of differentiation. 



3. The hemipterous and dipterous galls are prosoplasmas 

 or those forms of heteroplasias whose cells and particularly 

 whose tissue forms differ fundamentally from those of the 

 normal parts. Each of these galls shows definite specificity. In 

 the hemipterous forms the specific characters are in part 

 related to the plant structure which bears the gall; in the dip- 

 terous galls the specific characters are wholly related to the 

 specificity of the physiological phenomena associated with 

 the species of larvae concerned in the development of the 

 galls. 



4. In the prosoplasmas the types of cells found are closely 

 comparable to those of the normal plant parts, but the tissue 

 forms discovered are fundamentally new; no analogous structure 

 forms are to be found in the tissues of the normal plant or its 

 allies. 



5. In the dipterous prosoplasmas, since the gall's specific 

 tissue form characters are related to the species of insect, we 

 have the unique case of the "overlapping" of the hereditary 

 constitution of an animal on that of a plant in the sense that 

 factors associated with the insect determine the form character 

 locally, rather than those normally associated with the plant's 

 germ plasm. These latter plant factors suffer suppression. 



6. It is suggested that in the field of zoocecidology we 

 probably have a unique place, heretofore unrecognized, to 

 attack the problem pertaining to the mechanism used in the 

 expression of hereditary characters. 



