1864.] 565 



injured. It is by a careful study of what is truly and correctly speak- 

 ing the Skeleton of Insects, (so far as any part or organ in one Animal 

 Sub-kingdom can be homologous and homonymous with a similar 

 part performing similar functions in another Animal Sub-kingdom,) 

 and of the various confluences, counations, arrangements and shapes 

 of the bones, or " pieces," as they are commonly called, that compose 

 it. that most of the modern improvements in the Classification of Insects 

 have been perfected. 



The question naturally recurs here, how, having by the process de- 

 scribed above secreted this glutinous substance from the general sur- 

 face of its body, the larva of Cecidomyia contrives to detach itself from 

 it, so as to construct a true cocoon, enveloping its body, but not agglu- 

 tinated to that body. Winnertz declares that his larvee remained per- 

 fectly motionless during the process of the formation of their cocoon. 

 The larva, therefore, can scarcely become detached from the glutinous 

 matter by wriggling its body round and round, even if we could explain 

 how an insect, by wriggling round in a drop of tar, could form of that 

 tar a more or less thin pellicle, enveloping, but not agglutinated to 

 itself From the careful study of the phenomena presented by the co- 

 coons of the Willow Gall-gnats, I have arrived at the conclusion, that 

 after secreting the glutinous matter from the general surface of their 

 bodies, they must then discharge something of a gaseous nature, pro- 

 bably from the same pores which socreted the glutinous matter, so as 

 to detach the adhesive material from their external integument and 

 blow it up into a kind of bubble. We know that the imago of the Co- 

 leopterous Brachinus has the power of discharging a very acrid gas from 

 its anus, and that most plant-feeding Heteroptera in all their states dis- 

 charge a fetid gas from a large opening like a spiracle on the inferior 

 surface of their bodies. When in a particular species of Cecidomyia 

 the quantity of gas is small, then the cocoon is small, and fits pretty 

 closely to the body of the larva, as in the well-known Hessian fly and 

 Cec. s. brassicoides n. sp. When on the other hand, in another species, 

 the quantity of gas is large, then the cocoon is large as in Cec. s. stro- 

 hiloides n. sp. and its allies. When it is so large that it retains sufl&- 

 cient expansive force to press the cocoon firmly against the walls of the 

 cell, and those walls are adapted to adhere to a glutinous substance, 

 then the cocoon is firmly agglutinated to them, except at the elon- 



