506 Journal of Agricultural Research voi.v.no. 12 



of the blood of the host, these being retained in the stomach during 

 endoparasitic life, while the liquid parts, which are in excess, together 

 with the by-products of anabolism and katabolism formed in the body 

 of the rapidly developing larva, are eliminated by means of this enlarged 

 adaptive excretory organ, which is bathed by the blood at each cycle. 

 These by-products are doubtless eliminated from the body of the host, 

 as are its own, by the Malpighian vessels. The caudal vesicle no doubt 

 respires, this action taking place by osmosis, as is generally considered to 

 be the case in endoparasites having a closed tracheal system. Whether res- 

 piration is more rapid through the walls of the caudal vesicle or whether 

 they are especially adapted for it can not be positively stated, although 

 Weissenberg, as stated previously, thinks that the vesicle functions as a 

 blood gill. Again, that this portion of the body wall of the larv^a is 

 apparently the thinnest and least chitinized is quite evident; therefore, 

 it would not seem unreasonable to suppose that respiration takes place 

 to a large degree through this area and that the air is carried mechanically 

 throughout the body of the larva by the blood and is taken up from it 

 to fill the closed tracheal system when it develops in the second instar. 



Seurat's theory (7) that the essential function of the caudal vesicle is 

 that of locomotion is no doubt incorrect, for careful observations of the 

 movements of the larva show that the vesicle, because of its large size, is 

 actually a hindrance to the larva in moving about in its host. Weissen- 

 berg (9) has also shown that the caudal vesicle is not homologous with 

 the tail-like organs generally considered to be locomotor appendages 

 which occur in various endoparasites, for both these organs are present 

 in the larva of Macrocentrus sp. studied. 



An additional point brought out by Weissenberg is that the caudal 

 vesicle is an adaptation of the biophagous larva for its mode of life, for 

 the necrophagous larva does not have it, and these adaptations arise from 

 a biophagous mode of life in contrast with the necrophagous rather than 

 from an endoparasitic life in contrast with an ectoparasitic life, as has 

 been previously supposed. 



LITERATURE CITED 

 (i) Gibson, Arthur. 



1912. Cutworms and army-worms. Canada Dept. Agr. Div. Ent. Bui. 3 (Exp. 

 Farms Bui. 70), 29 p., 10 fig., i pi. 



(2) Henneguy, L. F. 



1904. Les insectes, Morphologic — Reproduction — Embrj'ogenie . . . 804 p., 

 illus., 4 col. pi. Index bibliographiquc, p. 695-756. 



(3) KoRSCHELT, Eugen, and Heider, Karl. 



1899. Textbook of the Embryology of Invertebrates . . . Translated from the 

 German ... v. 3, London. New York. 



(4) KuLAGiN, Nicolaus. 



1892. Notice pour servir a I'histoire du developpement des hymenopteres para- 

 sites. In Cong. Intemat. Zool. 2^ Sess. Moscou, pt. i, p. 253-277. 



