1906 ENTOMOLOGICAL SOCIETY. 



and the gall thus induced by the work of the larva is generally open ; while 

 the Cynipid, having a stinging ovipositor, deposits its eggs in the leaf 

 tissue through a minute puncture, which, quickly healing, leaves the 

 gall closed and the insect at maturity emerges through a hole which it cuts 

 in the gall, which the Cecidomyiid, on account of its sucking mouth parts, 

 is utterly unable to do. Here, moreover, we have an • explanation of the 

 apparently contradictory fact that Cecidomyiid galls are sometimes closed, 

 because whenever we find tins condition we invariably find the gall splitting 

 open at maturity. The reason for this in all probability is that the larva 

 entering the tissues makes a much larger incision than the minute puncture 

 induced by a Cynipid's ovipositor, and this, never completely healing, 

 splits open when the tissues commence to dry up in autumn. Similarly in 

 other orders the structure of the gall-maker determines the form of the gall. 



These abnormal growths have long been noticed and commented upon. 

 The earliest authentic work upon the subject was by Malphigi. In 168G 

 he published his "De Gallis," containing descriptions of a number of galls 

 common to Italy and Sicily. In America the subject was first taken up by 

 Osten Sacken, Walsh, Basset, Riley, Harris, and a few others who have 

 laid the foundations for most of our work on galls. Now a large number 

 of writers, among whom may be mentioned Ashmead in Hymenoptera, Per- 

 gande in Hemiptera, Garman in Phytoptidae and Norton in Nematinae. A 

 host of European writers have also taken up the subject, but in this country 

 there still remains an enormous amount of work to be done even in classi- 

 fication, while the morphology and histology is practically an unexplored 

 territory. 



The insects producing galls are confined principally to four orders, the 

 Acarina, which are not true insects but mites, the Diptera or flies, the Hem- 

 iptera or bugs, and the Hymenoptera including two families, the Tenthre- 

 dinidae and Cynipidae, and to a slight extent the Chalcididae. It is a curious 

 fact that the insects which are of the most developed and specialized struc- 

 ture, produce the most complex galls. That is, in the lower orders, as Thy- 

 sanura, the orders formerly included in Neuroptera, Orthoptera, and other 

 orders, we find no gall-making habits; while in the Diptera, Hemiptera 

 and Hymenoptera, and to a slight extent in the Lepidoptera and Cole- 

 optera we find the habit developed. This curious coincidence may be pos- 

 sibly explained thus — if, indeed, the lower and less specialized forms which 

 came into existence in an earlier age when a lower and now extinct type 

 of vegetation flourished, ever produced forms with the habit of gall-making, 

 these forms probably perished with the flora of that age, while the later 

 forms which now produce galls were evolved at a much later period when 

 the flora resembled that of the present age. 



The orders of insects among which we find the greatest number of gall- 

 producing insects are the Hemiptera, Diptera and Hymenoptera, and to 

 some extent the Coleoptera and the Lepidoptera. The order Acarina in the 

 class Arachnida contains the family Eriophyidae or gall-mites. These are 

 also specialized forms, inasmuch as acaralogists seem to be unable to agree 

 upon their relationship to other Acarina. 



Acarina. 



Family Eriophyidae, Gall-Mites. 



This is a family of microscopic mites which are quite curious and un- 

 usual in structure. They have only two pairs of legs and the abdomen is 

 long and striated. These striations, which differ in the different species, 

 and differ in number on the dorsal and ventral surfaces, are of considerable 



