History and Habits of Pityogenes. 41 
Leneru or Larvat Prrtop.— The length of the larval 
period in the laboratory, where conditions of temperature 
and moisture were fairly uniform, varied from eighteen to 
twenty-one days. Outdoors during May and early June, the 
larval period varied from eighteen to twenty-six days, there 
being several days when the temperature was such that little 
feeding was probably done. It is probable that a brood of 
larvae occurring in midsummer would require less than 
eighteen days for their complete larval history, and as we 
have already seen, individuals hatching in the fall may pass 
the entire winter as larvae, remaining in this stage for a 
period of eight months or more. However, a larval period 
of from eighteen to twenty-five days may be considered as 
about the normal one. 
Numser or Larvat Moutrs.— Regarding the number of 
moults during the larval stage fairly satisfactory observations 
were made. It was hoped to be able to establish the facts by a 
very careful microscopic examination of the refuse filling the 
larval burrows. In some cases the remains of five larval 
cast skins were found, four in the larval burrow embedded 
in the packed frass and one in the pupal chamber with the 
pupa. However, in other cases only one or two such larval 
exuvil were found. It is possible in these later cases that 
the larvae may have devoured their cast-off skins, as is known 
to be the habit of some other insects, or it may merely have 
been overlooked on examination of the frass. Until better 
evidence is at hand then, the author is inclined to place the 
number of larval moults at five. In a burrow 18 mm. long 
the cast skins were distributed as follows: The first 2.5 mm. 
from the egg niche, the second 5 mm., the third 8 mm., the 
fourth 12.5 mm., and the fifth in the pupal chamber. As 
will be seen, both the conclusions regarding the number of 
moults and also the place in the burrow at which each moult 
occurs, agrees very well with the data given in the table of 
measurements of larvae on page 39. There seems to be no 
good reason for doubting that normally there are five larval 
instars. If the larval period in the case cited above was 
eighteen days the moults would occur about as follows: The 
