INSECTA. 



975 



Fig. 432. 



a, part of the hepatic vessel of the larva of Sphinx 

 ligustri when nearly full grown, showing the 

 coeca ; b, part of the same in the pupa, the coeca 

 disappearing, 



Durckheim, and others. From each of these 

 supposed cceca in the larva of sphinx we have 

 traced an exceedingly minute and transparent 

 vessel which has appeared to be connected with 

 other delicate ramifications, and sometimes 

 with the immense quantity of adipose sacculi 

 with which the whole viscera are surrounded. 

 These Malpighian vessels undergo considerable 

 changes while the insect is passing from the 

 larva to the perfect state. The cceca begin to 

 disappear soon after the insect has entered the 

 pupa state (/>), and not a trace of them is dis- 

 coverable in the perfect insect, so that the 

 function of the organ is gradually diminished 

 in activity. During the larva state they exhibit 

 a remarkable peculiarity at their connexion -with 

 the alimentary canal which seerns to have some 

 reference to their function. It is a dilatation 

 at the point of union of these vessels in the 

 sphinx to form a single duct that opens into 

 the ilium, and if these be hepatic vessels may 

 represent a gall-bladder, as once observed to 

 us by Dr. Grant, but the exact function of the 

 vessels is very difficult to determine. The 

 following observation which we made in the 

 summer of 1832 and have since repeated seems 

 a little to show the nature of the contents of 

 these vessels, and also of other parts of the 

 alimentary canal. We gave sugared water, 

 coloured with indigo, to some specimens of 

 Vanessa urticte which had been confined for 

 several hours without food after they had left 

 the pupa state. On examining the insects 

 about two hours afterwards the stomach was 

 found filled with fluid containing a great quan- 

 tity of pink-coloured granules, which appeared 

 to be the vegetable indigo acted upon by the 

 acid contents of the stomach by which it had 

 become saturated, thus distinctly indicating the 

 presence of an acid in the stomach during 

 digestion. But it was remarkable that some of 

 the indino that had passed the pyloric extremity 

 of the stomach, where these supposed biliary 

 vessels enter, and had also passed throughout 

 the whole length of the ilium and even in part 

 into the colon, had been restored again to 

 its original dark blue colour, thus indicating 

 the presence of an alkalescent fluid secreted 

 either by the hepatic vessels or the ilium along 

 which the indigo had passed. But another 

 curious circumstance was that the hepatic ves- 

 sels also partook of the same pinkish hue as 

 the contents of the stomach, which seemed to 

 indicate that the contents of these also are acid. 



The conclusions we drew from these observa- 

 tions, which we repeated very carefully in 

 1834, were, that there is an acid gastric juice 

 secreted in the stomach during digestion, that 

 the contents of the so-called hepatic vessels are 

 probably also acid, and that an alkaline fluid 

 is secreted by the ilium, otherwise the indigo 

 reddened in the stomach could not have been 

 restored to its original colour. These circum- 

 stances seem to lead to the conclusion that the 

 Malpighian vessels are rather uriniferous than 

 biliary, more especially as they have been 

 found by Chevreul* and Audouinf to contain 

 uric acid ; but if this be really their function, 

 a question then arises why they are inserted so 

 near to the pyloric extremity of the stomach in 

 almost all insects, and the excreted fluid be 

 thus required to traverse nearly one-half of the 

 whole alimentary canal before it is ejected from 

 the body ? This consideration still inclines us 

 to suspend our opinion as to their true function, 

 and leads us still to believe that they may be 

 in some way connected with the function of 

 digestion and assimilation. 



The anal or proper uriniferoits organs. We 

 agree with Burmeister that the anal are the 

 true urinary organs. They do not in general 

 evacuate their contents directly into the canal, 

 but on each side of the anus. They exist, as 

 we have seen, in the Carabidee (fig. 424, s), 

 and their general form, as long ago shown by 

 Dufour in these insects, is that of a long vessel 

 convoluted upon the colon and emptying itself 

 into an oval or kidney-shaped vesicle on each 

 side of the colon, and terminating in a single 

 duct close to the anus. Dufour found the 

 minute vessel on the colon connected with an 

 aggregation of rounded glandular bodies, each 

 connected with the vessels by a very minute 

 filament, but we have overlooked this structure 

 in our own examinations. Neither have we 

 seen it in the Dyticidte, in which each urini- 

 ferous organ commences in two apparently 

 coecal tubes, which, after being a little convo- 

 luted, unite into one which empties itself into 

 a vesicle on each side of the colon and rectum. 

 Similar vesicles have been shown by Dufour in 

 the Stapkylinida, as in Staphylinus erythropterus 

 and in the Silphidte, in both which we have 

 ourselves distinctly seen them arising by a 

 single vessel which empties itself into an urinary 

 bladder on each side of the anus. In the 

 Silphida this bladder opens directly into the 

 termination of the rectum. 



The adipose tissue. -This tissue, which it is 

 necessary to allude to in connexion with the 

 organs of nutrition, consists of an immense 

 number of little transparent membranous vesicles 

 filled with opaque adipose matter, which, in 

 the generality of insects, is perfectly white, but 

 in others, as in the butterflies, is of a bright 

 yellow colour. The vesicles are usually very 

 irregular in form, being sometimes nearly oval 

 and at others elongated or triangular. They 

 communicate freely with each other and form 

 a most intricate web or reticulated structure. 

 They cover the whole of the abdominal viscera 



* Straus Durckheim,Considerat. &c. 1828, iv. 251. 

 t L'Institut. 133. 



