462 



COMPARATIVE ANATOMl" 



CHAP. 



of the hind-gut form a loop (Fig. 32-2). The 2 limbs of the loop grow together 

 for a certain distance, and wind round each other at this part. 



In the larvEe of some Hymenoptera, Ncuroptcm, MyrmeUon, and Diptera 

 (Pupipara) the mid-gut ends blindly and is not yet connected with the hind-gut, the 

 latter performing exclusively excretory functions (Fig. 321). 



The Malpighian Vessels.— These are long, generally filamentous appendages, 

 which begin to form as invaginations of the proctodieum. Their large epithelial 



Pic. 320.— Nervous, tracheal, and digestive systems of tlie Honey bee (after Leuokart). 

 The fine branchings of the tracheal system are not represented, the tracheal system on the right 

 side of the figure is only partly dra^vn. n n, Facet eye ; ct, antenna ; &i, 62, &3, the 3 pairs of legs ; th, 

 part of the tracheal longitudinal trunks swollen into a large vesicle ; st, stigmata ; Ttm, honey 

 stomach ; cm, chyle stomach : vm, Malpighian vessels ; rd, rectal glands ; ed, hind-gut. 



cells (with nuclei often branched) contain coloured concretions in which uric acid 

 is found. The Malpighian vessels occasionally have no distinct lumen ; they then 

 consist of a few rows of cells. The number of the Malpighian vessels is as varied 

 as their manner of entering the hind-gut. 



Apterygota. — Malpighian vessels are wanting in lapyx and the ColUmhola. In 

 Cmnpodea there are ca. 16, and they are here short ; in the other Thysmixira they 

 are long and 4-8 in number. The tubules always unite in pairs before entering the 

 hind-gut. 



Pterygota. — The Malpighian vessels are either very numerous and relatively short 

 or less numerous (2-8) and long. They are more numerous in the Dermaptera (ca. 



