INSECTA. 221 



mole-cricket and cockroach, they are very numerous. Dr. Burmeister 

 has generalised the observations of different anatomists on the bile- 

 tubes, as follows : — 



1. Four. 



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



tina, Psocina, and Mallophaga. 

 h. Anastomosing ; many Coleoptera, Hemiptera^ and Diptera. 



2. Six biliary vessels. 



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

 hycina and Chrysomelina. 



b. Free at the end ; Lepidoptera. 



3. Eight free biliary vessels ; Neuroptera. 



4. Many biliary vessels ; Hymenoptera, Orthoptera, and the Dic- 

 tyotoptera subulicornia. 



Those biliary vessels are longest which are fewest in number : they 

 lie in folds by the side of the stomach and intestine, and terminate in 

 a circle at the commencement of the small intestine. In LygcBus 

 apterus they terminate in a dilatation on one side of the gut. 



The urinary glands are usually in the form of long and delicate tubes, 

 but sometimes present the structure of groups of round vesicles, as 

 in the Carabiis, 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 termination of the in- 

 testine, or evacuated contiguous to the anus. 



No absorbent vessels have been detected in msects ; the chyle, 

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

 extending into other parts of the body and its appendages, resembling 

 the general interspaces of the cellular tissue, and constituting the 

 venous system, through which the blood moves in a definite and regular 

 course to the heart. This organ {Jig> 104. s) is an elongated muscular 

 and valvular tube, situated along the middle of the back, and usually 

 called the dorsal vessel : it is largest in the abdomen, and so dimi- 

 nishes anteriorly, that its continuation in the thorax may, in most 

 insects, be regarded as the aorta. It is retained in its position by 

 flattened triangular bands of muscular fibres. This character, its 

 distinct transverse linear muscular fasciculi, its slight constriction at 

 regular intervals, and the peculiar valvular loops at these constric- 

 tions, characterise the long and slender vasiform dorsal heart in the 



