74 GENERATION OF INSECTS 



ter in the light of reason, for neither milk nor cheese ever 

 grow wormy, if they are kept in a place secure from 

 flies; this is sufficiently proven by the experiments al- 

 ready made, and the contrary happens in case of expo- 

 sure to flies. As I recall certain things that I have ob- 

 served in connection with the breeding of worms, I shall 

 relate them to you, leaving out such as appear superflu- 

 ous and tiresome. 



I had placed half of a fresh cheese, the best to be found 

 in June, in a large, uncovered, glass dish; after a few 

 days several worms appeared in it, which upon examina- 

 tion seemed of two kinds; the larger were of the ordi- 

 nary sort produced on meat, and the smaller were of 

 the same shape, but had this peculiarity : they were more 

 spry and agile than the others; they moved about with 

 great ease, and would take their tails in their mouths, 

 thus forming a circle, or would skip here and there, 

 sometimes escaping from the vase. Three or four days 

 after birth all the worms ceased from motion, as usual, 

 and shrunk into eggs [pupae], differing only in size; 

 these I separated and placed in different vessels. After 

 eight days ordinary flies came out of the larger balls 

 [pupse], and from the smaller there emerged, after twelve 

 days, small flies resembling winged ants, which imme- 

 diately after birth skipped about with incredible spright- 

 liness and vivacity so that they seemed to be the em- 

 bodiment of perpetual motion. Then, every male pair- 

 ing with a female, performed those acts from which 

 propagation might be expected, but owing to lack of 

 nourishment they died after a short time. While mak- 

 ing this experiment I fortunately found a cheese that 

 had just begun to grow wormy, and after separating 

 the good part from the bad I enclosed both in separate 



