Physiology of H&m at o^inus tenuirostris, Burm. 91 



not be employed in this case, on account of the opaque epider- 

 mis. Finally I succeeded in preparing it from specimens 

 which had lain for months in dilute alcohol. 



The dorsal vessel (vas dorsale) consists of a fine tube which 

 stretches, in the direction of the middle line of the animal, 

 close to the integument of the back, about from the extremity 

 of the abdomen to the middle of the anterior margin of the 

 thorax. So far I could trace it ; but it is certain that it does 

 not terminate there, but passes further up into the head 

 (fig. 13, a). The tube presents on both sides a great number 

 of appendages, some of which adhere to it by broad surfaces, 

 while others are connected with it only by narrow tubes 

 (fig. 13, c). These appendages run in multifarious convolu- 

 tions, with frequent constrictions, parallel to the sides of 

 the animal to the belly, where they seem to terminate 

 cascally. At its posterior extremity the tube widens into a 

 peculiar vesiculiform organ, presenting numerous muscular 

 bundles, which lie annularly around it. We also observe in 



it many elongated fibres running from in front backwards, pro- 



bably longitudinal muscles. A little before its posterior ter- 

 mination this organ shows on each side a strong muscular 

 bundle, by which it is attached to the integument of the back. 

 We also observe further in the middle and at the upper end 

 of the vesicular structure several strong muscular bundles on 

 both sides, which serve the same purpose as those above 

 mentioned. But as regards the tube itself in its further course, 

 I have nowhere observed upon it any trace of muscles which 

 could effect its attachment to the dorsal integument. It is there- 

 fore to be supposed that in this case the whole dorsal vessel 

 is not, as in other insects, attached to the integument of the 

 body by means of numerous muscles which at the same time 

 produce the pulsating movement, but is connected therewith 

 by muscles only at its posterior, and perhaps at its anterior 

 extremity, and otherwise hangs down freely into the body- 

 cavity. The tube itself, as also the vesicular organ at its 

 hinder extremity, appears much darker than the above-men- 

 tioned appendages, the colour of which is a dingy grey. The 

 walls of the tube are closed throughout their length, and only 

 give off small narrow canals into the appendages (fig. 13, b). 

 The contents of the tube are finely granular j as to the 

 structure of its wails I can say nothing. The appendages, on 

 the other hand, present a fine clear membrane, which is per- 

 forated by numerous quadrangular, pentagonal, and hexagonal 

 apertures. Over these is stretched a second layer, which ex- 

 hibits innumerable extremely fine granules. Upon the appen- 

 dages we also detect numerous irregular longitudinal and 



7* 



