THE PHOTIC KE ACTIONS OF SARCOPHAGID FLIES 173 



though it is viviparous northward. This difference in habit has 

 been pointed out by Portschinsky ('85) for Musca corvina, which 

 always deposits eggs in the neighborhood of St. Petersburg, though 

 in southern Russia it is usually viviparous in the summer (see also 

 Osten Sacken/87). 



For convenience in reference I shall designate the stages'* into 

 which the life-history of the flies in question naturally fall, as 

 follows : 



a. The egg stage, representing the period from the extrusion 

 of the egg to the time of its hatching. 



h. The larval stage, extending from the time of hatching until 

 pupation. This stage is sharply divided into two periods by the 

 migration of the larva from the flesh upon which it has been feed- 

 ing, to bury itself in the earth or among debris. These two periods 

 I shall designate as (1) the feeding period and (2) the prepupal 

 period, the latter being usually referred to as the resting stage. 

 From the standpoint of habits these two periods are quite distinct 

 and it is therefore not sufficient to refer merely to the time of 

 infancy as the larval stage. The first few days after hatching are 

 distinctly a period of excessive feeding (Herms '07, pp. 57-67 on 

 normal growth), and the days immediately preceding pupation 

 are not strictly a resting period, since the larvae are quite active 

 under conditions to be described later. However, they do not 

 feed during this time even when after weeks of starvation they are 

 given the opportunity. Hence it seems preferable to refer to this 

 simply as the prepupal period. This period, of all periods of the 

 life-history of these insects, is subject to the greatest variation in 

 length due mainly to changes in temperature and moisture (Herms, 

 '07, p. 52). 



c. The pupal stage which is distinctly a quiescent stage so 

 far as locomotion is concerned. Before the pupal case has become 

 opaque, if light is thrown on the animal, movements of the inter- 

 nal organs can clearly be seen. Muscular connection with the case, 

 is however, soon severed and locomotion is no longer possible. The 

 disintegration of the larval tissues takes place ordinarily in from 



*For the duration of these stages the reader is referred to table 1. 



