AND ANATOMY OF CERTAIN HYMENOPTERA PARASITICA. 



411 



Some SiJeculations xoitli regard to the Morphological Identity 

 of the Vesicle o/' Microgaster. 



Those authors who have examined these remarkable hirvse unanimously 

 agree that the vesicle is the ninth abdominal segment, much enlarged. For 

 one thing, I consider that these previous observers are incorrect in saying it 

 is the ninth ; as a matter of fact, even if it is really a segment, it is, I 

 think, the tenth abdominal segment. But one is forced to question whether 

 the bladder really is a segment. 



Where is the proctodseum ? Where are the Malpighian tubules? What 

 is the homology of the vesicle glands ? 



14 



■K.J::: 



Fig. 12. Arrangement of the meseuteron (M), Malpighian tuhules (MP), proctodaeum (PD), 



anal gland (AG), and gonad (G) in typical insect larva. 

 Fig. 13. Position of these organs vs^hen the proctodaeum is evaginated ; compare positions of 



letter X in both figures. Fig. 13 represents the condition found in the 



Microgaster larva. 

 Fig. 14. Stomodseal lining. 

 Fig'. 15. Mesenteron lining : both to same scale. 



These questions alone serve to put us on our guard against the too rapid 

 acceptance of the view that the bladder is a segment. In text-figs. 12 & 13 

 I give two drawings illustrating my tentative conception of the bladder as 

 true proctodaeum turned inside out. In text-fig. 12 the mesenteron (M), 

 Malpighian tubules (MP), anal glands, and proctodseum (rectum) are shown 

 in the ordinary position found in many insects. In text-fig. 13 the letter X 

 drawn in the previous figure has shifted its position, and the outside of the 

 vesicle is now what was really the inside of the rectum in the previous figure. 

 By this evaginative process, the anal glands (AG) become placed just as the 



