The Life History of Drilus Jiavesecns. 43 



the entrance. While the summer lasts, the undeveloped 

 larva, as a rule, evacuates the shell about forty days after 

 entering it, and goes off in search of another. Excluding 

 the shorter feeding interval (July to September) in the 

 year of hatching, it may thus devour as many as three, 

 or perhaps four snails in the course of the summer, 

 moulting once in each case before leaving the shell. But 

 it often ceases feeding as early as July, and in one example, 

 at least, under notice this year, the first shell entered by 

 the larva on June 2nd, after hibernation, was not left after- 

 wards. In such cases the larva, on moulting, reassumes 

 the winter form (which is referred to below), and the 

 growth is again suspended until the following year. From 

 examples under observation, this early return to the winter 

 form seems to be caused by a period of low temperature 

 preceding the time of moulting. An instance of it occurs 

 in the following incomplete record of a remarkable larva : 



1900, July 8th: Larva (length about 8 mm.) entered 



H. virgata (greatest diameter 8 

 mm.) ; 



1901, May 30th : evacuated this shell (length about 



10 mm.), and entered H. aspersa 



(greatest diameter 8 mm.) ; 

 „ July 10th : left this shell (length about 13 mm.), 



and entered H. aspersa (greatest 



diameter 28 mm.) ; 

 „ August 18th: left this shell (length 21 mm.), and 



entered //. aspcrsa (greatest 



diameter 25 mm.); 

 ::,j „ 31st: seen to be cleaning out this shell 



(length, at the time, fully 30 mm.). 

 Unfortunately, in the spring of 1902, it died while still 

 in the winter stage. The larva was doubtless hatched in 

 July 1899, and must therefore have become full-fed in 

 the third year, as seems to be more often the case. 



The winter form, into which the undeveloped larva 

 changes about the middle of September, or often earlier, 

 as stated, is incapable of feeding or of more than a heavy 

 grub-like motion, Avhen disturbed. In general outline 

 it much resembles the ordinary form of the larva, but it 

 rather perhaps deserves the term "false pupa." The scuta 

 are absent, the body being almost entirely soft, of a dingy 

 whitish colour, and, except on the last three or four 

 segments, almost hairless. The head is small, rather soft, 



