196 The University Science Bulletin. 



DEVELOPMENT OF MALE GENITALIA. 



(Plate XIX, figs. 2, 4, 6, 8, 10, 12; Plate XX, figs. 1-18.) 



The male genitalia, consisting of three pairs of valves arise from 

 a genital area on the ninth abdominal segment. In the first, second 

 and third instars there are two pairs of valves present. These de- 

 velop in small chitinous pockets, which are attached at the caudal 

 edge of the genital area with their apices directed caudad. The 

 genital area increases slightly in size in each successive instar, as do 

 the pockets. The pockets are placed one upon the other, the ven- 

 trally placed pocket producing the plates of the adult and the more 

 dorsal pair the oedagus. The ventral pair is about twice as long as 

 the dorsal. Both taper caudad, and are somewhat rounded at the 

 apex. Each pair is divided into its right and left valve by a chit- 

 inous median partition. 



In the fourth instar there is, as in the former instars, a noticeable 

 increase in size, both of the genital area and of the ventral and dor- 

 sal pockets. In addition to these structures, there is now present a 

 pair of small lateral pockets located at the lateral margin of the 

 genital area, and extending caudad as far as the bases of the dorsal 

 pockets. In these lateral pockets develop the styles of the adult 

 genitalia. In the fifth instar there is no great change in the relati^'e 

 position and shape of the pockets. There is, of course, a natural 

 increase in the size of all three pockets. 



In the fifth instar the greatest changes in- the developing genital 

 appendages take place. The three pairs of valves may be traced 

 through several distinct phases of development by a study of the 

 soft, white integument which can be drawn from the chitinous pock- 

 ets. Details of five particular phases might be mentioned. (Plate 

 XX, figs. 6-18.) 



The ventral plates which develop in the ventral pockets show 

 very little change throughout the successive phases of this instar. 



The styles which develop in the lateral pockets are present in all 

 five phases and show a gradual increase in size through the phases. 

 In the fourth phase they first show their permanent attachment to 

 the ventral plates, which is more apparent in the fifth phase and in 

 the adult. They are attached on their outer edges near the base of 

 the plate. 



The developing oedagus or the integument drawn from the dorsril 

 pockets shows the most remarkable alterations. In phase 1 the 

 cedagus consists of two valves placed parallel to the ventral plates. 



