Dec. 20, 1915 
Biology of Apanteles militaris 
505 
species of Macrocentrus studied was equipped with a tracheal system, 
while the corresponding stage of A, glomeratus was not. The conclusion 
is drawn that the vesicle functions as a blood gill in A. glomeratus , since 
all the blood necessarily pours through this vesicle, bathing its walls, 
while in Macrocentrus sp., which possesses a tracheal system, such an 
adaptation is not necessary. 
An unknown species of the genus Limneria, parasitic on Plutella 
cruciferarum Zell., is next introduced for comparison by Weissenberg. 
In this parasite the portion of the proctodeum homologous with those 
of the two preceding larvae discussed is not so well developed, for while 
pseudopod-like structures extend into the anal lumen, they do not pro¬ 
trude through the anal opening, which, however, is nevertheless very 
large. In this species it is clearly shown that the cells of these pseudopod¬ 
like structures completely correspond histologically with those of the 
larval Malpighian tubules. In a similar manner these specialized por¬ 
tions of the proctodeum of the two species last discussed are reduced 
and the portions retarded grow rapidly, approaching the normal procto- 
deal development of free-living larvae before pupating, the normal proc- 
todeal development of Hemiteles fulvipes , an ectoparasite of A . glom¬ 
eratus, being used in comparison to illustrate this. 
In the last analysis it is seen that the cells of these proctodeal append¬ 
ages of the three endoparasitic larvae considered are histologically allied 
with the cells of the larval Malpighian vessels, and with this in mind 
Weissenberg brings out clearly the idea that these proctodeal organs 
have also an excretory function and credits Kulagin (4, 5) with first 
suggesting this from results obtained from his injection experiments. 
Weissenberg further thinks that the excretory apparatus has undergone 
a superficial enlargement, owing to the active metabolism characteristic 
of this group, and that as excretory products in general are poisonous, 
it would seem natural to find here an adaptation by which they can be 
eliminated. His concluding argument is that in A . glomeratus , Macro¬ 
centrus sp., and Limneria sp. the development of the larval Malpighian 
vessels forms an ascending series, they being only rudimentary in A . 
glomeratus in comparison with the well-developed ones found in Limneria 
sp., while the proctodeal adaptations form a descending series, being 
most highly specialized and developed in A. glomeratus and only partly 
so in Limneria sp. 
From the facts presented above and this study of A . militaris , the 
author concludes that the caudal vesicle is primarily an excretory organ 
and that the function of respiration is secondary. The following observa¬ 
tions seem still further to strengthen this conclusion. The caudal vesicle 
functions from approximately the beginning of feeding to its close, and the 
portion of the first skin molted which covers the vesicle becomes greatly 
swollen in the second stage with a liquid content until finally it is ruptured. 
Further, the food of the larva is mainly the already digested solid parts 
