The Great Water-Beetle. 427 



higher animals. The true urinary organs, at least in Dyticus 

 are probably represented by the vessels usually denominated 

 " anal." They are double, each consisting of a delicate tor- 

 tuous tube — the kidneys — which leads to a bladder from which 

 proceed an excretory duct. The colour of these organs is 

 generally of a bright sulphur in those specimens I have 

 examined. They are situated near the amis, on each side of 

 which they appear to pour out their contents. 



How, it may be asked, are the nutritious products of diges- 

 tion assimilated by insects which do not possess any lacteal 

 system, as occurs in the Vertebrata, nor veins, which in the 

 Mollusca absorb the nutritive materials ? The chyle is 

 supposed to pass through the walls of the intestine and to 

 become mixed with the blood in the cavity of the body. 

 " This transudation has, indeed, been actually witnessed," we 

 are told, " by Ramdohr and Rengger, and even analysed by 

 the last-mentioned physiologist, who found it to consist almost 

 entirely of albumen.-" 



The examination of the anatomy of insects is attended 

 with very great pleasure to the student of Natural History, 

 but, at the same time, it must be confessed that much difficulty 

 besets his investigations, and there is need of a large stock of 

 patience and perseverance. The best thing to do is to select 

 several large species of the different orders, and begin upon 

 them ; it is advisable, also, to make one part of their organiza- 

 tion the object of more especial study. The Dyticus marginalis 

 might be taken as a type of the internal structure of the 

 Coleoptera ; a dragon fly (Libelhda or (Eschna) of the 

 Neuroptera ; a cockroach of the Ortlwptera ; a sphinx moth of 

 the Lepidoptera ; a humble bee of the Hymenoptera. By this 

 means a general knowledge will be obtained which may be 

 improved by a more extended examination of different species 

 of the same orders. Burcneister's Manual, and old Swammer- 

 dam's Book of Nature, together with Newport's valuable paper 

 on Insects in Todd's Cyclopaedia, with Rymer Jones' General 

 Outline of the Animal Kingdom, will be found useful to the 

 physiological entomologist. 



The figure which illustrates the- digestive apparatus, it 

 should be stated, represents the intestinal tract in a straightened 

 form. The whole portion from the stomach to the anus in its 

 natural position in the insect is considerably twisted. The 

 pendent portion on the right side of the stomach is part of 

 the adipose matter ; not a salivary gland, for which it might be 

 mistaken. 



