426 The Great Water-Beetle. 



matter passes into the bulbous body (the jproventriculus) 

 where it undergoes trituration by means of a series of horny 

 spiues or teeth, eight in number, readily recognized by its 

 yellow colour. The jproventriculus which is very muscular, 

 evidently corresponds to the gizzard in birds. From the 

 jproventriculus the food descends to the stomach or ven- 

 triculus ; herein, from the presence of a number of in- 

 vesting secreting organs, it is evident that the food is more 

 fully prepared for assimilation. If we open the jproventriculus 

 by a finely-pointed pair of scissors, and examine a portion of 

 its internal surface, we shall see that these glands communicate 

 with it, and doubtless pour into it a secreted fluid. To the 

 stomach succeeds the duodenum, into which two pairs of 

 anastomosing filaments of a chocolate colour run. Then 

 follows the ilium and the colon, the distinction between 

 which, however, are not always very apparent.* The com- 

 plicated lines of a brown colour, which twist around a 

 large part of the whole intestinal tract, are usually called the 

 biliary vessels. In insects, to quote the words of Milne 

 Edwards, " there exists no liver, properly speaking, but this 

 organ is replaced by long and delicate tubes which float in the 

 interior of the abdomen and open superiorly into the chyle- 

 forming stomach. These biliary vessels also take the place of 

 urinary glands, for it is here that the uric acid is formed." 

 These vessels are supposed by some writers to correspond 

 rather to the kidneys of the higher animals than to their liver. 

 " If we consider these organs as kidneys," Van der Hoeven 

 observes, " it becomes uncertain whether insects have a liver ; 

 for the idea that these vessels may represent at once both 

 kidneys and liver (whence it has been proposed to name them 

 vasa urino-biliaria) , is not, as appears to me, the result of 

 comparative investigation, either anatomical or physiological, 

 and would never have been entertained but for the attempt to 

 reconcile two conflicting views, and which ought always to be 

 distrusted when it interferes with more extended inquiry." 



Van der Hoeven gives some reasons for believing that the 

 encircling fatty matter may represent the liver of higher 

 animals. " Since the production of fat," he adds, " exerts the 

 same influence on the composition of the fluids as the sepa- 

 ration of bile, it is not to be considered as a proceeding 

 entirely arbitrary, if some recognize in the adipose body an 

 analogon of the liver." There does not, however, seem to be 

 any reasonable doubt that the term " biliary " is correctly 

 ascribed to these organs, and that they represent the liver of 



* Careful focussing with £ inch objective reveals the presence of three distinct 

 membranes throughout the entire length of the intestinal tract, but their nature 

 and form will not be understood without drawings. 



