CH. i] INTRODUCTORY 7 



the point of the head comes in contact with the shell. 

 The movements of the prisoner make a slight split in 

 the egg-shell, which then bursts asunder. This organ 

 has vanished in later larval life, and it is probably 

 lost after the first moult. The larva is legless and 

 has thirteen segments. It grows rapidly, and, as it 

 grows, moults its skin several times. It is provided 

 with mouth-parts adapted for biting, and eats any 

 decaying organic refuse. The larvae may be reared on 

 the sweepings of an ordinary room or the dirty scurf 

 which collects at the bottom of old birds' nests. It 

 is hardly necessary to add that the mother takes no 

 interest whatever in the larvse and that the belief 

 that she feeds them on dried blood is not based on 

 any sound foundations. 



The larval stage lasts some days, and the animal 

 spins a small cocoon before pupating. In the course 

 of a few more days, the time probably depending on 

 the weather, the perfect flea emerges. The larvae 

 generally live in places where the perfect insects will 

 have an opportunity of finding a host as soon as 

 they leave the pupal envelope. The nests of their 

 hosts where the young are being reared are always 

 favourite places. It seems possible that the com- 

 parative immunity from fleas which hoofed mammals 

 or Ungulates enjoy may be due to the fact that the 

 young beast follows its mother from the time of birth 

 instead of passing its early life helpless in a nest. 



