THE DIGESTIVE EPITHELIUM OF DRAGONFLY 



NYMPHS. 



JAMES G. NEEDHAM. 



IN the aquatic nymphs of dragonflies the alimentary canal 

 fills a role of unusual importance. It chews, digests, excretes, 

 and respires. More than its name implies, it is in a broad sense 

 an organ of nutrition, or, rather, it is a series of nutritive 

 organs. Its anterior third is concerned with the comminution 

 of the food; its posterior two-fifths with excretion and respira- 

 tion, and the small remaining middle portion, the ventriculus, 

 alone digests the food, and, according to Cuenot, 1 also alone 

 absorbs it. Recognizing its small size in proportion to the size 

 of the body, and recalling the voracity of these insects, one is 

 prepared to find in it conditions of exceptional activity. 



In the dragonflies the ventriculus (mitteldarm, mcdi-intestin} 

 is a simple tube without caeca or diverticula of any sort, slightly 



FIG. i. Alimentary canal of Gomplius tfescriftus Banks, side view, tracheae removed, x 2. P, pre- 

 intestine; S, stomach, ventriculus, or mid-intestine ; J//', Malpighian tubules: i and 2 divi- 

 sions of the post intestine ; G, gill chamber; K, terminal portion of the rectum. 



narrowed posteriorly to its junction with the intestine at the 

 origin of the Malpighian tubules. At its anterior end it meets 

 the pre-intestine by a deep circular invagination into which the 

 end of the so-called "gizzard" (valvulc hophagienne) descends. 

 Its walls are of nearly uniform structure throughout, consisting 

 of four well-marked layers which are, passing from within out- 

 ward, (i) a layer of epithelium (not quite a simple layer, as we 

 shall see); (2) a membrana propria, or basement membrane; 

 (3) a layer of circular muscles; and (4) an incomplete layer of 



1 CUNOT, 1895: fitudes phys. sur les Orthopteres, Arch, de Biol., xiv. 



