112 Journal of Agricultural Research voi. iv. No. a 



Bolle^ and Prowazek (ii). Prowazek found that pepsin hydrochloric 

 acid dissolves the polyhcdra of the silkwomi, and Bolle found that the 

 juices of silkwonn intestines dissolve them likewise, so that it is not at 

 all improbable that the gipsy-moth caterpillars digest polyhedral bodies 

 very rapidly. 



The only things found within the intestinal lumen of caterpillars are 

 partly undigested leaf cells and occasional bacteria. The latter are 

 sometimes found in great numbers in the intestines of caterpillars raised 

 on abnonnal food in the laboratory, but they are scarcely ever found in 

 sections through diseased individuals taken in the field. Lettuce was 

 frequently fed to caterpillars hatched in the laboratory in the winter, but 

 this is unfavorable food, as cultures showed, being full of bacteria of all 

 sorts, especially when after standing it begins to ^ferment. That bac- 

 teria are not etiologically related to wilt will be shown more definitely in 

 this paper. 



PATHOLOGY OF THE BLOOD 



Before considering the blood of diseased gipsy-moth caterpillars, the 

 various elements in the lucmolymph of normal individuals should be care- 

 fully distinguished. For purposes of microscopical examination a drop 

 of blood can be best obtained by pricking one of the caterpillar's prolegs 

 with a fine needle. In healthy animals the blood is clear; light yellow in 

 males and greenish in females.^ 



The morphological elements or blood corpuscles are represented by two 

 main types. Those of the first type are the ordinary round or amoeboid 

 cells, amoebocytes (PI. XIV, fig. i, 2). An actual pseudopod-like 

 streaming has never been obser\'ed, but, since we find such forms as shown 

 in Plate XIV, figure i, with foreign bodies within them (phagocytosis), 

 there can be little doubt as to their mode of progression. Graber's view 

 (8) that the form of the leucocyte is due as much to the various blood 

 sinuses as to its own individuality is not held by the writer. Graber says 

 that the blood corpuscles are elastic, but that on their squeezing through 

 narrow passages or sinuses this elasticity is broken down — that is, the 

 corpuscles reach their elastic limit and are unable to reassume their 

 natural sphericity. Hence, the various ama?boid and stellate cells are 

 due to the shape and width of the passages traversed. It is, however, 

 generally accepted that the blood corpuscles in most insects move in an 

 ama^ioid manner, thus resembling the leucocytes of man. 



All of the blood corpuscles of insects possess a nucleus, and the leu- 

 cocytes of the gipsy moth are no exception to this rule. The nucleus is 



' cited by Prowazek (ii). 



- For these interesting se.xunl differences in the color of caterpillar blood see the following papers: 



Geyer, Kurt. Untcrsuchungen iibcr die chemische Zusaminensetznng der Insektenhiimolyniphe und 

 ihre Bcdeutungfiir die geschlechlliche Diffcronziening. In Ztschr. Wiss. Zool., Bd. 105, Heft 3, p. 349-499, 

 fiE- 58, pi. 20-23. Literatiirverzcichniss, p. 4SS-.)99. ig'S- 



Stechc, O. Beobachlungen iibcr Gcschlechtsuntcrschicde der Hiiniolyniph von Insektenlarv-cn. In 

 Verhandl. Deut. Zool. Gcsell., Bd. 32, p. 272-381. 1912. 



