262 



Illinois State Laboratory of Natural History. 



slowness of movement, and loss of appetite. These are later to 

 appear than the pale discoloration above mentioned, and even 

 shortly before death a larva may show considerable impatience 

 if roughly handled. When the disease is well developed, the 

 caterpillar is very feeble, and will remain motionless for a 

 long time ; or if it attempt to crawl where some strength is 

 needed, as horizontally on a vertical surface, it may lose its 

 hold with its jointed limbs and cling only by its central prolegs, 

 the fore and hinder parts hanging limp and helpless at right 

 angles to the remainder of the body. 



Most commonly an escape of fluid from the vent is among 

 the earlier symptoms of the affection, at first greenish or whit- 

 ish, and later a dirty gray, or even a chocolate brown. Rarely 

 this fluid exudes also from the mouth. The amount of it is 

 usually sufficient to stain considerably the surfaces over which 

 the larva crawls: but sometimes this symptom is wholly absent. 

 Occasionally the stomach is found empty after death, but almost 

 invariably it is well filled with food, much of which has not yet 

 lost its native color, digestion being, in fact, evidently sus- 

 pended during the course of the disease. I have found in only 

 a single instance an appearance of bubbles of gas in the alimen- 

 tary canal, such as Pasteur describes in the Jlacherie of the silk- 

 worm. Usually the mass of the alimentary contents seems to 

 lie inert in the stomach, undergoing neither digestion nor 

 deca}^ 



The color of the fluids of the healthy larva is a very pale 

 transparent green, the blood containing only lymphoid cor- 

 puscles in greater or lesser number; but if a proleg of a dis- 

 eased specimen be snipped off, and a cover glass be pressed 

 against the cut surface, the droplet exuding will be of almost 

 milky whiteness, or, in the latest stages of the disease, a dirty 

 gray. Rarely, where there has been much escape of fluid from 

 the vent, the juices of the larva will be thick and scanty, so that 

 it requires some pressure to force out a very small quantity. If 

 a minute droplet of the milky fluid obtained by snipping off a 

 proleg be examined under a high power of the microscope, it 

 will found to contain innumerable myriads of very minute 

 spherules, varying in diameter, according to the individual, from 

 .5|utol/t. Usually their average size does not surpass .7 ;U.. It is 



