INSECT A. 381 



cricket and cockroach, they are very numerous. Burmeister has 

 generalised the observations of different anatomists on the Mal- 

 pighian tubes, as follows: — 



1. Four. 



a. Free at the end ; most Diptera, and the families Termi- 



lina, Psocina, and Mallophaga. 

 h. Anastomosing ; many Coleoptera, ffemiptereij and Diptera. 



2. Six tubes. 



a. Anastomosing ; many Coleoptera ; for example, Ceram- 

 bycina and Chrysomelina. 



b. Free at the end ; Lepidoptera. 



3. Eight free tubes ; Neuroptera. 



4. Many tubes ; Hymenoptera, Orthopterd, and the Dictyoptera 

 subulicomia. 



Those Malpighian tubes are longest which are fewest in number : 

 they lie in folds by the side of the stomach and intestine, and ter- 

 minate in a circle at the commencement of the small intestine. In 

 Lygeeus apterus they terminate in a dilatation on one side of the 

 gut. 



Uric acid has been detected * in these tubes : they have no proper 

 epithelial lining, but are filled with cells, disposed in rows: these 

 cells contain mucus and numerous fine granules, which impart 

 a yellowish or greenish colour to the tubes. The granular 

 contents pass by rupture of the discharged cells into the intestine, 

 and may be found accumulated in the colon or caecum : they are 

 ultimately evacuated with the faeces. K no biliary principle be 

 eliminated together with the uric acid from the Malpighian tubes, 

 they are, nevertheless, by the character of their connections, relative 

 position, and place of development from the alimentary canal, the 

 homologues of the hepatic organs. The glands, which by the same 

 morphological characters are more strictly urinary, are usually in the 

 form of long and delicate tubes, but sometimes present the structure 

 of groups of round vesicles, as in the Carabus, in which the common 

 duct terminates in a small dilatation : the urinary bladder is likewise 

 present in the water-beetles. The excretion is poured into the ter- 

 mination of the intestine, or evacuated contiguous to the anus. 



No absorbent vessels have been detected in insects : the chyle, 

 which is a clear or greenish fluid, with round or oval corpuscles, is 

 supposed to transude through the tunics of the intestine into the 

 free cavity of the abdomen : it passes, in reality, into the wide and 

 irregular sinuses which seem to constitute the cavity of the abdomen, 

 but which communicate with similarly ill-defined venous receptacles 



♦ CCXLVIL A. p. 629., B. p. 213. CCXLII. p. 251. 



