22 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 
hooklets. The larva stretches its segments apart, and then contracts 
them, waves of extension and contraction passing anteriorly. The 
ventral hooklets prevent the segments from slipping backwards, and 
locomotion results. 
Dr. C. B. Bridges has dissected the gonads from numerous fully 
grown larve. He finds that they are situated between the third and 
fourth main lateral branches of the longitudinal tracheal trunks, 
counting from the posterior end. Each gonad is embedded in a fat- 
body, one lying on each side of the body of the larva. The ovary at 
this stage is a very small spherical body, somewhat more transparent 
than the surrounding fat-body. The testis is much larger, ovoid, and 
quite transparent. 
The fully grown larve of Drosophila cardini and of D. saltans ‘‘skip”’ 
in the same way as.do those of Piophila and a few other Acalyptere 
(e. g., Hpochra among the Trypetine). The larva bends around and 
grasps its posterior end with its mouth-hooks. The body is then 
straightened and the hooks pull loose suddenly. The body straightens 
immediately, and is thus caused to spring several inches into the air. 
I have not observed any morphological structures of the larve asso- 
ciated with this curious habit. This habit has been looked for in very 
many other species, but I have not yet found it, except in the two 
forms just named. Malloch (1915) has, however, reported it in a 
species of Drosophila bred by him. 
The larva of Drosophila busckit bears, on the dorsal surface of each 
segment from the fourth to the twelfth, about eight branched processes 
similar to those present on certain anthomyiine larve. This is evi- 
dently the form figured and described by Riley (1918) as found in 
milk-bottles. 
In the genus Scaptomyza the bands of ventral hooklets are less 
distinct than in most species of Drosophila. In Chymomyza the an- 
terior band is not evident. 
Drosophiline larve differ from some other described acalypterate 
larve in having the posterior spiracular openings on definite raised 
processes. This condition is found in Hydrellia (Ephydrinz) and 
Leucopis (Ochthiphilinz) by Keilin, and in a species of Agromyza by 
Webster and Parks, but does not occur in the numerous species of 
Calyptere, Ortaline, Trypetine, and Piophiline studied by Banks. 
PURZ:. 
Drosophila, like other cyclorhaphous Diptera, pupates within the 
last larval skin. The fully-grown larva crawls out of the food, appar- 
ently in nature coming to rest usually in the loose surface soil. The 
anterior spiracles are extruded to form the ‘‘horns”’ of the puparium, 
as the combined pupa and larval skin is called. The larval skin, at 
first soft and white, hardens and turns brownish in the course of a few 
