May, 1916] Morphology of the Zoocecidia of Celtis 255 



If the tissue of the heteroplastically changed organs and parts 

 of organs be compared with corresponding normal tissues, 

 differences will be found in more than one connection; the 

 abnormal tissues vary from normal ones in regard to size of 

 the single elements, as well as to the degree and kind of 

 differentiation." 



In the mind of the writer, the "degree and kind of dif- 

 ferentiation" of tissues is the most significant with particular 

 reference to the form assumed by the heteroplastic tissues 

 as opposed to the forms of similar tissues in the normal parts. 



Heteroplasmas, Kiister divides into two sub-divisions, 

 " Kataplasmas (differentiation not widely different from the 

 normal) and " Prosoplasmas " (differentiation definitely and 

 specifically different from the normal). The acarinous and 

 lepidopterous galls (one each) to be described hereafter fall 

 under the first, while the hemipterous and dipterous forms are 

 all excellent examples of the second. 



In the description of the galls, the taxonomic characters will 

 be presented first, followed by the discussion of the histology. 



In conformance with a previous paper (Wells [33]) the new 

 galls described are not named, but given a list number. As 

 pointed out in that paper it is essentially unscientific to name 

 an insect with only the gall at hand. No entomologist would 

 feel justified in creating a species on the characters of a 

 puparium or coccoon, for such a structure embraces but a 

 small part of the total number of characters to be considered. 

 Only the paleo-entomologist should have the privilege of 

 dealing in fragments. While it can be shown that the specificity 

 of the galls is related to the specificity of the adult insects, this 

 relation is not a causal one, but is merely a relation established 

 through the fact that both gall and adult insect have a common 

 specific origin in the larva. If the entomologist is to properly 

 describe his unit (species) he should have all of the differentia- 

 tion products coming out at the end of the insect's ontogeny. 

 Too frequently, the entomologist has ignored the gall as a 

 "deformation," when it is often as specific as the antennas in 

 its form and structure characters. 



