150 Journal New York Entomological Society. [^'°i- x>^x. 



rotting weeds, by Bremi from cow dung, while Dufour states that 

 he obtained it from ulcers in elms. My larval specimens of Gco- 

 sargiis z'iridis were found by the late Prof. M. V. Slingerland living 

 in the richly fertilized soil of a potted green house plant. The 

 specimens described by Malloch were obtained from cow dung. 



Some larvc-e found in cow dung, but not reared, when placed in 

 caustic potash and later examined showed plainly through the in- 

 tegument the next succeeding instar. By careful manipulation it 

 was possible to draw out the inner skin which proved to be quite 

 similar to that of G. viridis making allowance for future expansion. 

 The penultimate instar thus differs strikingly from the final instar, 

 the depressed scale-like hairs being characteristic. The heads ol 

 these are shown in figures 32 and 37. This form is designated as 

 Sp. A in the key. 



Some larvje closely resembling the foregoing but differing in the 

 form and armature of the head (fig. 35) were found associated with 

 the G. dccorus larvse in Dr. Needham's experiment. Their form, 

 and body covering of depressed hairs indicate that they are the 

 penultimate instars of Gcosargus, and probably of G. dccorus. 



Figures 27 and 30 are details of the larva of Macrosargiis clavis 

 Will., while fig. 31 shows the head of its penultimate instar. Dr. 

 P. W. Claassen discovered these larvae living in the frass of the larva 

 of Ar::ai>ia obliqiia which infests cattail stems. The earlier stage 

 was found in July, the last instar in April and May, of the following 

 year, adults appearing in May and June. There appears to be but 

 one brood which hibernates as larvae in the last instar. The pe- 

 nultimate instar has body markings similar to, but feebler than, the 

 last instar; the latter lacks the appressed scale-like hairs which the 

 former possesses. 



The last two instars as well as bred specimens of the adult flies 

 of Microchrysa polita were obtained in July by Dr. Needham from 

 the vegetable matter used in the experiments above mentioned. I 

 have also reared this species from cow dung. The form described 

 by Malloch as " Genus Incertus 3 " is without much doubt the pe- 

 nultimate instar of M. polita. This instar is usually marked in a 

 similar manner to that of the last instar, though sometimes the pat- 

 tern is but feebly indicated. European writers record the rearing 

 of this species from cow dung and decaying vegetable matter. 



