Contagious Diseases of Insects. 317 



narrower towards one extremity. Nuclei about one half as 

 long and wide as the cells containing them were visible in 

 most. Neither cells nor nuclei stained readily with aniline. 



The blood of many of the larvae examined contained also 

 considerable numbers of mulberry cells of rather large size, 

 composed of granules averaging about 2 /* in diameter. 



As no insects affected by muscardine had been handled by 

 us at the time these caterpillars were received at the office, it is 

 certain that they brought the infection with them; and as all 

 perished, without exception, from this same disease, and this 

 without the development of spores by which the contagion 

 might have been conveyed from one to another, the presump- 

 tion is very strong that the affection illustrated by these indi- 

 viduals was that which had swept away the greater part of the 

 entire brood of the preceding year, and especially that which 

 had caused the death of the young larvae as reported by Mr. 

 Ayres. 



SUMMARY AND CONCLUSION. 



The circumstances under which the studies above described 

 have been made; the fact that they belong to a field of research 

 so difficult that new comers are very properly viewed with a 

 certain suspicion until they have clearly demonstrated their 

 right to labor in it; and the further fact that my results have 

 not always emerged from the cloud of experiment with per- 

 fectly clear and definite outline, have seemed to me to require in 

 this paper a quantity of detail sometimes amounting, perhaps, 

 to wearisome prolixity; and the following summary of the 

 principal features and results of my research has been prepared 

 in the hope that it may serve to make this mode of treatment 

 less objectionable. 



I have first attempted to characterize a common and highly 

 destructive disease of the European cabbage worm (Pieris 

 rapce), by whose ravages the injuries of these pests have received 

 a very important check, a disease especially marked by the 

 whitish color of the living larvae, amounting before death to 

 an ashy or almost milky hue, and by a rapid post mortem black- 

 ening and decay. The distinguishing microscopic appearances 

 are, first, a remarkable whiteness and opacity of the circulating 

 fluids which are early loaded with immense numbers of very 



