120 ON THE ANATOMY OP THE FLY. 



diately afterwards are more difficult to observe, but after the 

 second day of the pupa state, numerous delicate nebulous- 

 looking cells, about l-1000th of an inch in diameter, replace 

 some of these aggregations, and bright nuclei, l-3000th to 

 l-5000th of an inch in diameter, make their appearance amongst 

 them. The majority of the aggregations remain, however, 

 and become more dense toward their circumference. The 

 growth of the imaginal tissues evidently proceeds at the ex- 

 pense of some of these aggregations, whilst those which remain, 

 undergo marked changes ; they increase in size, lose their 

 original nuclei, and become invested by a delicate membrane. 

 When the imago emerges from the pupa, a large number of 

 these corpuscular aggregations remain in all parts of the 

 insect ; they disappear during the development of the imago, 

 and when it is mature, not one can be detected. I propose the 

 term growth-corpuscles to designate these remarkable bodies. 



The growth-corpuscles of the imago, when it emerges from 

 the pupa, vary from l-80th to l-200th of an inch in diameter. 

 They contain molecules and granules of various sizes, besides 

 numerous nucleated cells, l-1000th of an inch in diameter, with 

 a well-defined cell wall, and from one to three large nuclei. 

 The exact manner in which these corpuscles are concerned 

 in the development of the tissues is, at present, unknown ; their 

 functions may be similar to those of the folliculate glands, the 

 preparation of the nutritive fluid or formative plasma. I do not 

 think they are directly converted into tissue either in the pupa 

 or imago. 



All these changes are much influenced by temperature, and 

 the entire development of both the mature larva and the pupa 

 in all its stages is immediately stopped when the temperature 

 falls below 45 Fahrenheit. This circumstance alone preserves 

 the species through the winter, all the larvae and pupse existing 



