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 identi- 

 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 

 lengthwdse, 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 



