10 Psyche [February 
Within the thorax a clear specimen shows a number of parts: 
the anterior lobes of the heart with a large valve, the contractions 
of which synchronize with the throbbing between the trachee of 
the abdomen; the beginning of the arch of the trachez, surround- 
ing the food tube, and from which branches are later given to the 
organs of the thorax; the three pairs of imaginal buds. 
Within a few hours after the first molt, one larva was eating 
vigorously of fine filaments of algee, and preferably of surface 
particles. It swallowed the filaments from the end, just as does 
the full-grown larva. 
By the time the larva is six days old, it begins to show signs of 
the approaching second molt, which occurs from the seventh to 
ninth day. As before, the head becomes narrow and the “collar” 
dark and broad. One measured 2.2. mm. at this time, making a 
growth of .7 mm. in about two days. 
Third Stage of the Larva (fig. 5). The most important changes 
which are evident after the second molt are: the rapid increase in 
the size of the thorax accompanied by the enlarged internal organs; 
the appearance of the ommatidia of the adult eye, around the 
larval eye; the disappearance of two pairs of the long hairs and 
the general shortening of all the thoracic hairs; the darkening of 
the integument of the head, which shows an unexpected pattern 
in the maculation. Eight specimens examined at this age showed 
almost exactly the same arrangement of pigment on the head. It 
may not be constant, but it is certainly more so than that of any 
other stage. 
Respiratory Siphons (figs. 17, 18, 19). At this time it is possible 
to see, along with the rapid growth of the wing buds, the forma- 
tion of the pupal respiratory siphons in the prothorax. From the 
time of the first molt, a pair of straight tubes in each side of the 
thorax has been evident. Now they have become more conspic- 
uous. They seem to change their position, sometimes being close 
up to the anterior wall of the thorax, and sometimes they le with 
the end quite away from the wall. Developing near by, at an 
angle with the first tube, and penetrating also through the wall, is 
another structure, tube-like at first, but after a time changed to 
form a part of the now plainly visible respiratory siphon. The 
siphons, also, are frequently drawn away from the integument, 
at other times being pushed up close to it. 
