536 Cc. H. RICHARDSON 
still be seen on the anterior portion of the first segment. The 
reduced mandibles cross the mouth opening which is surrounded 
by a chitinous ring. The color of the larva is now light blue- 
white. The larger part of the body is occupied by the mesen- 
teron which appears as a dark mass. The mouth opening com- 
municates with a short, wide pharynx, into which the narrow 
oesophagus opens. This portion of the digestive tract is lined 
with a very perceptible chitin. Surrounding the food mass in 
the mesenteron is a very weak peritrophic membrane composed 
of but one loosely assembled layer of chitinous granules. The 
short, wide proctenteron ends blindly against the wall of the 
mesenteron. Dorsally to this lie the small paired ovoid gonads. 
The long salivary glands reach beyond the posterior end of the 
mesenteron. The oval adipocytes and the large larval oenocytes 
are present in this stage. The tracheal system is undifferen- 
tiated and the lateral tubercles so characteristic of the larval 
stage to follow are entirely absent. The name atracheate larva 
is given because of the lack of a tracheal system. No traces of 
a heart could be found. 
The atracheate larva is a sessile parasite, never voluntarily 
changing its position upon the host and giving its entireattention 
to feeding and growth. Very slight movements of the body can 
often be detected, but the larva is quite unable to crawl. If 
it be carefully watched, deep peristaltic waves can be seen travel- 
ing from the anterior to the posterior end of the mesenteron. 
These are often so marked that the adipocytes can be seen shift- 
ing back and forth in the body cavity. 
THE TRACHEATE LARVA 
At the end of from thirteen to seventeen days, the curious 
lateral tubercles and rudiments of the tracheal system appear, 
marking the beginning of what I shall call the tracheate larval 
stage. This third larval form varies in length from 2 to 4 mm. 
and its greatest width is about 55 per cent of the length. The 
first segment is greatly retracted, especially in the larger indi- 
viduals. The antennal tubercles and mandibles persist and a 
