NO. 14 



INSECT ABDOMEN SNODGRASS 



43 



overlapping plates (oostegites) that grow over the thoracic venter 

 from the bases of the legs, but in some species it is formed by anterior 

 and posterior folds of the ventral integument, and in others by an 

 invagination or a series of sacklike ingrowths of the membranous 

 ventral wall of the thorax. In one genus, Paragnathia, the young are 

 said to develop in the ovaries, which serve as uteri. 



The Amphipoda are provided with a pair of small penes, but they 

 have no organs of sperm intromission ; the eggs are fertilized outside 



Gprs XnStn XmStn 



Pen 



Stn 



Trtpd 



■~-Expd 



■"~-Endpd 



E 



t6. — Crustacea-Malacostraca-Peracarida : male genitalia of Isopoda and 

 Amphipoda, 



A, Scrolls (isopod), ventral view of last thoracic and first abdominal seg- 

 ments, showing gonopores on sternum of somite XII. B, Gammarus locusta 

 (amphipod), ventral view of last thoracic segment, showing penes arising at 

 bases of coxopodites. C, Porccllio laevls (isopod), testis and exit duct of one 

 side, and median penis. D, same, penis and first pleopods, ventral view. E, 

 same, second pleopods. 



Brn, branchia ; Cxpd, coxopodite ; Dct, genital exit duct ; Endpd, endopodite ; 

 Expd, exopodite ; Gprs, gonopores; Pen, penis ; Prtpd, protopodite ; Stn, sternum ; 

 T, tergum ; Tcs, testis ; Vsm, vesicula seminalis ; XllStn, sternum of male genital 

 segment ; XlllStn, sternum of first abdominal segment. 



the body of the female. The penes, as illustrated in Gammarus locusta 

 (fig. 16 B, Pen), are a pair of short cylindrical processes arising from 

 membranous areas between the lateral arms of the last thoracic ster- 

 num and the bases of the coxopodites. During mating the male at- 

 taches himself to the back of the female and remains in this position 

 until the female moults ; then immediately the male curves his body 

 under that of the female and attaches small masses of sperm to the 

 body wall of the latter in the neighborhood of the oviducal apertures. 

 The eggs, later extruded, are fertilized in the brood pouch beneath 



