22 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 



booklets. The larva stretches its segments apart, and then contracts 

 them, waves of extension and contraction passing anteriorly. The 

 ventral booklets prevent the segments from slipping backwards, and 

 locomotion results. 



Dr. C. B. Bridges has dissected the gonads from numerous fullj' 

 grown larvae. 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 gro^\^l larvae of Drosophila cardini and of D. saltatis "skip" 

 m the same way as do those of Piophila and a few other Acalypterse 

 (e. g., Epochra among the Tr j^Detinse) . 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 larvse 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 husckii bears, on the dorsal surface of each 

 segment from the fourth to the twelfth, about eight branched processes 

 similar to those present on certain anthomjiine la,TY£e. 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 booklets are less 

 distinct than in most species of Drosophila. In Chymomyza the an- 

 terior band is not evident. 



Drosophiline larvse differ from some other described acalj^pterate 

 larvae in having the posterior spiracular openings on definite raised 

 processes. This condition is found in Hydrellia (Ephydrinae) and 

 Leucopis (Ochthiphilinse) by Keilin, and in a species of Agromyza by 

 Webster and Parks, but does not occur m the numerous species of 

 Calypterae, Ortalinae, Trypetinae, and Piophilinae studied b}- Banks. 



pup;e. 



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 lar\^al skin, at 

 first soft and white, hardens and turns bro\\Tiish in the course of a few 



