194 University of California Publications in Zoology [Vol. 19 



at ease. They again huddled closely together as formerly, the mother 

 bird sitting on them during the night. 



During the next few days a number of other experiments were 

 carried out with this brood of goldfinches. "While one of them was 

 being held in the hand, a few vigorous, half grown larvae were placed 

 among the nestling's feathers. After crawling about among them for 

 a brief period, the larvae would invariably drop from the bird. One 

 evening several dozen, half grown, hungry larvae were put in a paste- 

 board box and covered with a layer of soft cotton about an inch thick. 

 Two of the nestlings were then placed on the cotton and the box 

 closed. In less than ten minutes eight of the larvae were found firmly 

 attached to the two nestlings, ingesting blood, only a few releasing 

 their hold while the birds were being examined. This last experiment 

 was repeated the following afternoon, but none of the larvae were 

 found attached to the birds. "When this experiment, however, was 

 repeated in the evening, and on subsequent evenings, some of the 

 larvae were found attached to the nestlings. This indicates that the 

 larvae are mainly active at night and that they probably rest in the 

 lower parts of the nest during the day. It may be of interest to note 

 that both of the nestlings that were used for these experiments died 

 several days later, apparently from loss of blood. 



During the eleven weeks over which this investigation extended, a 

 careful study was made of the activity of the larvae and the resulting 

 flies; these have been since identified as Protocalliphora azurea 

 (Fallen) by Mr. C. "W. Johnson, curator of the Boston Society of 

 Natural History. The larvae were kept in pasteboard boxes, in some 

 of which soft cotton or bird-nest material was placed. They usually 

 crawled about until they had found a secluded, dark spot, the crevices 

 between the layers of paper of the boxes being their favorite resting 

 place. 



In these pasteboard boxes various organic substances were placed, 

 such as fruit, bread, meat, and boiled potato. Although the fly larvae 

 crawled through some of these substances, they fed upon none of them. 

 One day I secured a large bone containing many blood cavities. 

 Among these blood cavities I bored several holes and placed the bone 

 in a box containing several dozen fly larvae. The latter had been 

 starved for about a week so that there was not the slightest trace of 

 food left in their intestines. The next morning I found two or three 

 of them with fresh traces of blood in their alimentary canal, conclusive 

 evidence that they had been feeding upon the ox blood contained in 



