1868.] 91 [Trouvelot. 



localities a more prominent appearance. The under surface resem- 

 bles a thin membrane tightly stretched, and is of a lighter shade than 

 the rest. The vent is prominent, subconlcal, situated about .05 in. 

 above the row of cilia, and darker in color. 



The living larva differe only from the pupa-case in color, being of 

 the tr;msparent white of the garden shrub called snowdrop, with the 

 exception of the reddish-brown tulvercles, vent, and ciliated border, 

 and in the mobility of the under surface by which it progresses in a 

 precisely similar manner to the larva? of the LimacodidiE. The head 

 is visible only as a minute retractile pair of black mandibles, under a 

 strong magnifier. The last three to five days before its pupation two 

 darker round spots appear under the transpai'ent skin opposite, and a 

 little above the level of the vent; when the insect is fairly in the pupa 

 stage, each spot has taken the form of a little conical cluster of 

 tubercles, slightly protruding from the surface. These organs appear 

 to serve as spiracles during the pupa stage, communicating by delicate 

 tubes with the body of the enclosed insect between the head and pro- 

 thorax. The imago effects its exclusion by separating the anterior 

 third of the pupa-case into three divisions, the upper forming two 

 comma-shaped pieces, each containing a spiracle, and tlie lower a 

 single vase or salver-shaped piece. The insect belongs to the family 

 Syrphidae, genus Microdon of Meigen, Aphritis Latreille, and the 

 species was named globoKu.'i by Fabricius. His descri^Dtion was very 

 brief, and has been apparently transferred word for word by all 

 subsequent authors. 



Mr. L. Trouvelot offered the following observations on the 

 comparison of young larvre of insects. 



It is quite interesting to compare together, in the early stage of life, 

 lepidopterous larvae belonging to different species of the same genus; 

 the resemblance is sometimes so striking that it is not an easy matter 

 to separate one species from another. 



I think a comparative study of recently hatched larva?, belonging 

 to the same genus, would lead the entomologist to the knowledge of 

 the degrees of relationship which exist between different species of 

 the same genus' and then, to the degree of relationship between 

 genera. Insects, and particularly Lepidoptera and some Ilyuien- 

 optera, seem to be better adapted for this comparative study than 

 any other class of aniuials, since the larval stage is only the ani- 

 mal in a yet undeveloped or embryonic .«tate. and as this embryo 



