160 
Larvae of Fleas 
At the end of the larval period, just prior to the spinning of the 
cocoon, the larva becomes less active ; it is of a more opaque white 
colour than before, and the body is shorter and fatter, and with a more 
conspicuous tapering of the ends. The increase in size in larvae of 
Xenopsylla cheopis, as determined from the measurements of two 
drowned specimens, is as follows : 
Newly hatched Full fed, 
hut still active 
Length .. .. .. 2'0 mm. 4 - 5 mm. 
Thickness .. ., .. 0'22 mm. 0'47 mm. 
Length of head .. .. 0T6 mm. 0’21 mm. 
During this increase in size the larva moults twice. The average 
length of a full fed, active larva of Xenopsylla cheopis in the living state 
is 4 - 2 mm. (average of 15 observations). 
The remarks which follow refer particularly to active full-grown 
larvae, after the second moult and before the development of that excess 
of fat which indicates the approach of the pupal phase. The species 
examined in detail are: 
Pulex irritans Linn. 
Xenopsylla cheopis Rothsch. 
Ctenocephalus canis Curtis. 
Ceratophyllus fasciatus Bose. 
Ceratophyllus gallinae Schrank. 
Leptopsylla musculi Duges. 
Habits of Larvae. 
Except in the case of Leptopsylla musculi, the larvae of fleas are 
very active, moving with remarkable celerity through and upon the 
debris of the nests and dry rubbish among which they live. While 
naturally active, they become very excited and impatient when dis¬ 
turbed. The larvae, however, have periods of quiescence, during which 
they he coiled up in the manner of a watch-spring, either for repose or 
concealment; on the other hand, when about to moult they he stretched 
out at full length. 
When moving quietly, the larva crawls over an even surface sup¬ 
porting the body on the ventral hairs or setae, and extending and con¬ 
tracting the segments after the manner of an earthworm. Each seta 
can be moved independently of the others, as may be seen by watching 
