504 
Journal of Agricultural Research 
Vol.V, No. 12 
young larvae beneath tufts of grass. Considering the data at hand, the 
theory is advanced that in the North the parasites winter as partly 
developed forms in immature larvae, while in the South they no doubt 
also winter while in the cocoon. 
ORIGIN AND FUNCTION OF THE CAUDAL VESICLE 
The following is a summary of the results of the studies of Weissenberg 
and Seurat, together with the observations made by the writer, on the 
origin and function of the caudal vesicle, obtained mainly from experi¬ 
ments with hymenopterous endoparasites. 
As Seurat’s (7) and Weissenberg’s (9) papers both deal with A . 
glomeratus , the caudal vesicle of which originates and functions ident¬ 
ically as does that of A . militaris , the results of their studies are appli¬ 
cable to A. militaris. Weissenberg’s paper, being the more exhaustive 
and, in addition, containing studies of the larva of this parasite in 
comparison with others less highly specialized, is used as a basis for this 
summary. 
Observing the beginning of growth and the subsequent expansion of 
the caudal vesicle, the writer supposed that the entire proctodeum 
evaginated and turned inside out, but the careful histological studies of 
A. glomeratus by Weissenberg show that only a portion of the procto¬ 
deum through rapid growth becomes specialized to form the vesicle, 
while the remainder becomes temporarily atrophied. According to 
Weissenberg, the vesicle is formed by the rapid growth and elongation 
of the cells of the proctodeum which form the posterior end of the plug 
at the posterior end of the stomach, together with those adjacent cells 
at the anterior end of the proctodeum which surround the opening of the 
larval Malpighian tubules and extend posteriorly a short distance to the 
rudiments of the adult Malpighian tubules. The mass of elongated cells 
thus formed grows out through the anal opening of the embryo, and 
immediately following hatching these elongated cells are compressed 
lengthwise, so that their long axis becomes their short one, resulting in 
broad, flat cells joined edge to edge to form the thin wall of the caudal 
vesicle. During the rapid growth of these cells in the pyloric region the 
remainder of the proctodeum becomes atrophied and stays so until the 
caudal vesicle is drawn in. At this time parts specialized for endo- 
parasitic life are reduced, and the atrophied parts grow rapidly, the 
whole approaching the normal proctodeal development of a free-living 
hymenopterous larva, previous to pupation. 
Weissenberg next compares the origin and cellular structure of the 
caudal vesicle of A . glomeratus with that of the caudal appendage of the 
endoparasitic larval form of an undetermined species of Macrocentrus, 
and shows them to be homologous. In Macrocentrus sp., however, the 
cells always remain as a mass of long, slender cells protruding through 
the anal opening, a vesicle never being formed. The early stage of the 
