Jan. 15, 1920 Further Studies of Sorosporella uvella 431 



ments, is relatively thin. Furthermore, it is generally stated that this 

 layer of chitin extends into the mouth and anus, lining the intestine in 

 both these regions. There is, however, a relatively small portion of the 

 intestine, the mid gut, which is supposed to be of different origin from 

 the fore and hind gut, and which is said not to be lined with this substance. 

 The tracheae, a ramifying system of spirally reinforced tubes opening 

 externally in the spiracles, are likewise lined with chitin, though this sub- 

 stance is exceedingly thin, espec^'ally in the ultimate portion of the tubes. 



It is apparent, therefore, that of the regions where the germ tubes 

 might enter the body cavity, all save the mid gut are protected by an 

 inert, resistant substance through which the germ tubes must penetrate. 

 For this reason especial care has been taken to examine the mid gut in 

 prepared sections of inoculated individuals. 



It was deemed a matter of considerable interest, both from the scien- 

 tific and economic points of view, to know exactly how and where infection 

 takes place; and several tests have been carried out with the view of 

 determining this point. There are certain portions of the body wall in 

 which the chitin is comparatively thin, such, for example, as the inter- 

 segmental membranes, the flexible leg joints, etc. Furthermore, the 

 glandular openings and hair follicles are apparently less perfectly adapted 

 to resist the penetration of the conidial germ tubes than are most parts 

 of the body. Likewise it would seem quite possible for the small conidia 

 to gain entrance into the body through the spiracular openings of the 

 tracheae, and once inside to germinate and cause infection. The intestine 

 is, as stated above, lined for the most part with chitin, though this sub- 

 stance is relatively thin in most places and entirely absent in the mid gut. 



With these regions of possible infection in mind, artificial inoculations 

 were arranged in such a way that conidia came in contact with all por- 

 tions of the external body wall and the intestine, and bits of fungus mass 

 were also carefully placed on the tip of a needle directly in contact with 

 the spiracles. In order to introduce the conidia into the alimentary 

 tract, cutworms were fed with clover leaves which had been smeared with 

 the fungus ; and to place the conidia in contact wdth all external parts of 

 the body wall, a bit of conidial agar paste on the tip of a needle was 

 rubbed about over the body, although to facilitate subsequent micro- 

 scopic examinations of sections of the larvae it was often applied particu- 

 larly to the dorsal and ventral medial lines of the body. 



To examine the tracheae after inoculation, it was found advantageous 

 to dissect these organs from the body and mount them directly in 

 alcohol. Although a large number from many insects were examined 

 microscopically, the writer was quite unable ever to find conidia in them. 

 The examination revealed, however, the presence of chitinous spiny 

 bristles at the opening of the spiracles and clustered at various points 

 along the lumina of the tracheae, and when these were found it became 

 evident that they would effectively prevent the entrance of conidia. 

 153426°— 20 3 



