ON PSYCHOPTERA PALUDOSA. 73 



consist of ribands of cellular tissue containing fat-globules, which, 

 from their great number and minute size, refract the light strongly. 

 This tissue is that in which the material which is partly used up in 

 the pupa stage is deposited, and in consequence not much of it is 

 found in the perfect insect. 



The transformations of this insect resemble strongly those of 

 the Crane-Fly. Before the conclusion of its larval life, the growing 

 limbs of the pupa may be seen beneath the larval integument of the 

 thoracic segments, as roughly indicated in Fig. ii. The differences 

 between the mode of development of the Crane Fly and the Blow 

 Fly have been already described by me in a paper read before the 

 Quekett Microscopical Society,''' and the remarks therein applied 

 to the Crane Fly will be equally applicable to this insect. Unlike 

 the coarctate pupa of the Blow Fly, that of this insect sheds its 

 larval skin and has its limbs exposed, as seen in Figs. 3 and 1 2, and 

 this seems to be connected with a more gradual and less radical 

 process of internal change. The larval tissues do not undergo the 

 total degeneration and reconstruction that they appear to do in 

 the Blow Fly, and the pupa retains a small amount of voluntary 

 motion. 



In the pupa, as well as in the larva, the most curious part of 

 the structure of this insect is its respiratory organs. Lyonet states ■ 

 that the respiratory trunks of the body and their continuations into 

 the tail are left behind in the larval skin ; and he goes on to 

 express great surprise that the respiratory tail of the larva changes 

 its place in the pupa, and instead of being found, as heretofore, a 

 continuation of the abdomen, takes a new departure from the 

 thorax of the insect, immediately behind the head. This arises 

 from a misapprehension due probably to imperfect optical appli- 

 ances. His explanation of this subject is almost amusing, did we 

 not recollect the disadvantages under which he laboured, as 

 compared with the facilities of modern microscopic research. I 

 will give it in his own words. He says, " Quoique cette queue 

 dans I'etat de ver soit plus grosse et bien de la moitie moins 

 longue que dans I'etat de nymphe, on ne saurait pourtant douter 

 que Tune et I'autre ne soient le meme conduit de la respiration et 



* See "Journal of the Quekett Microscopical Club," Jan., 1876. 



