Contagious Piseases of insects. 301 



THE WALNUT CATERPILLAR. 

 {Datana atic/usi, G. & R.) 



I have to report under this species a series of observations, 

 cultures, and experiments, the longest which I attempted. 

 Although these failed, in part, of their original purpose, they 

 brought out incidental and unintended results of considerable 

 interest, and seem to me worthy of somewhat detailed description. 



On the 14:th of August, 1883, a lot of the larva3 of Datana 

 angusi were collected from a black walnut tree (Juglans nigra) 

 in the university grounds at Normal, and brought to the office 

 for experiment. Seven of these were placed in a breeding cage 

 in the further end of the Laboratory, somewhat removed from 

 all the other experimental lots. On the 30th of August one of 

 these was found dead in the cage, having certainly perished since 

 the preceding day. The body of this individual was very limp and 

 flaccid and considerably shrunken, and no food occurred in the 

 alimentary canal. Mounted slides of the blood show vast 

 numbers of the short, broad Bacillus, with rounded or sub- 

 truncate ends and pale central area, which I have distinguished 

 as Bacillus vntrapallens. The blood was, in fact, a nearly or 

 quite pure culture of this organism, only some smaller and 

 apparently undeveloped forms being possibly micrococci, but 

 more probably the above Bacillus in its earlier stages. These 

 bacilli measured upon an average 1.25 i^ by 2.5 /«, and occurred 

 singly and in doubles, the doubles with truncate oppostd ends 

 and broadly rounded free extremities. Besides the above, the 

 intestinal contents presented spherical micrococci, usually 

 single, but occasionally in process of division, .8 ^ to 1 /it in 

 diameter. I strongly suspect that these apparent micrococci 

 also were the above Bacillus intrapallens, undeveloped. 



The next morning a second larva of this lot was found 

 dead, having apparently succumbed several hours previously. 

 The intestinal fluids contained a great variety of bacteria, 

 including Bacterium, and multitudes of minute spherical 

 micrococci; but no slides or precise descriptions were prepared. 



On September 2 another larva died which had been ailing 

 for two or three days. But very few bacteria were found in 

 the blood, while the intestinal fluids were full of double ovals, 



