GLASGOW SOCIETY OF FIELD NATURALISTS. 157 



lines in galls formed by other animals. But all, so far as is known, 

 feed on vegetable matter, and there are no examples of species 

 which feed npon the substance of other insects, as we find in the 

 Hymenopterous Cynipidce, species of which are parasitic upon 

 the true gall-makers of their own group and in some instances 

 upon other insects. Certainly we find Cecidomyious larvse inhabit- 

 ing galls not formed by them, but by mites, as, for example, the 

 larvse of C. peregrina, Winn., found in the woolly mite-galls on 

 ThymuB serpyllum ; these have been observed to lick eagerly the 

 secretions or excretions of their hosts, but no evidence has been 

 found — the dried skins of mites, for instance — to show that they 

 ever devoured their hosts. 



I cannot leave this part of my subject without referring to a 

 remarkable discovery made in the summer of 1861 by Professor 

 "Wagner of Kasan, that of the asexual reproduction of the larvse 

 of a Cecidomyid which lived gregariously beneath the bark of a 

 tree. Inside certain of these larvse germ-cells were formed, from 

 which larvse were developed — a number in each parent larva. 

 These lived upon the tissues of their host and in due time emerged 

 from what had at last become an empty skin, giving birth in 

 their turn to other larvse ; until the cycle was completed by the 

 larvse becoming pupse and producing the perfect insect, which laid 

 properly fertilized eggs, the larvse from which would in their turn 

 reproduce in this asexual way for a period. Pagenstecher, Meinert, 

 Ganine, and Von Baer have confirmed it. For details I would 

 refer you to the abstracts which appeared (with illustrations) in the 

 " Annales des Sciences Naturelles " for 1865. Grimm has recorded 

 similar facts in the pupa of a gnat, Chironomus sp. We have here 

 an example of what has been termed by Steenstrup " Alternation 

 of Generations " — a form sexually producing an unlike form, which 

 reproduces itself asexually, ultimately completing the cycle by 

 assuming the first form. This reproduction in the preparatory 

 stages of development has received from Von Baer the designation 

 of " Psedogenesis." 



It may be interesting to mention here that the once dreaded 

 Hessian-fly is a Cecidomyid, very aptly named by the American 

 entomologist Say, C. destructor. For an account of its habits I 

 must again refer you to the pages of Kirby and Spence. 



The larva of the Gecidomyidoe assumes the pupa state sometimes 

 within the gall, but often leaving it and entering the ground ; and 



