36 Linnean Societij. [May 1, 



noptera, as noticed in the first part of this paper, in these larvae of 

 Paniscus. It occurred at least three times in each larva before 

 quitting its shell. The skin is burst as in other insects along the 

 dorsal surface of the thorax, and is gradually carried backwards 

 chiefly by the effect of growth of the larva, but it continues to in- 

 close the caudal segments, which are also included between the two 

 halves of the shell. The fourth change occurs when the insect is 

 transformed to a nymph. It assumes this state inclosed in a leather- 

 like cocoon spun by itself after it has destroyed the caterpillar on 

 which it has fed, and while lying in the earthen chamber which the 

 caterpillar had formed for its own change under ground. The change 

 to a nymph took place in April, and to the perfect Ichneumon fly, 

 Paniscus virgatus, in May 1848. 



The author then describes the mode in which the alimentary canal 

 is originally developed in the embryo of insects. The first developed 

 portions of the embryo are, first, the ventral, and then the lateral 

 parietes of the segments. The lateral grow from below upwards, 

 until their free margins ultimately approach along the future dor- 

 sal surface, meeting first of all in the cephalic, and then in the cau- 

 dal segments. The termination of the future alimentary canal in 

 the anal segment is the result of a fold on itself of a layer of the 

 first portion of the yolk included by the completion of the two cau- 

 dal segments, and is the commencement of the column of cells, 

 which afterwards becoming perforated when the larva is full grown, 

 form the colon and intestine, and which retains the celliform struc- 

 ture to so late a period in the larva of Monodontomerus . The re- 

 mains of the yolk are included within the body by the union of the 

 segments along the dorsal surface, and form the digestive cavity, 

 the last portion included being in the prothorax, at which point the 

 yolk enters the body in Crustacea, as pointed out by Rathke. The 

 mode in which the great digestive cavity, or stomach, and the dif- 

 ferent structures of the canal are formed is then described, and the 

 general configuration of the organ is shown to be very similar, during 

 the earlier stages of growth, in all embryos of insects. This pri- 

 mary form is longer retained in the imperfect apodal larvse, espe- 

 cially in the parasites, than in other species, and hence the incom- 

 pleteness noticed in Monodontomerus. The structure is completed 

 earlier in Microgaster and Ichneumon ; but although in these a true 

 colon and intestine are formed these continue closed, and no faeces 

 are passed until the larva is matured. The appendages of the canal 

 follow the same laws of development. The glands which produce 

 the silk required by the insect for the formation of its cocoon, are 



