ARACHNIDA. 



311 



doubt, be regarded as a reservoir of nutriment ; and when the ha- 

 bits of these animals are considered, the precarious supply of food, 

 and the frequent necessity for long-protracted fasts, when a scar- 

 city of insects deprives them of their accustomed prey, such a 

 provision is evidently essential to their preservation. 



(357.) One peculiarity connected with the arrangement of the 

 chylo-poietic viscera of the spider is the manner in which the biliary 

 organs terminate in the intestine ; for instead of entering in the 

 usual position, namely, close to the termination of the stomach, 

 they seem to pour their secretion into the rectum immediately in 

 the vicinity of the anus. At this point, a kind of sacculus (figs. 

 142 and 143, f) joins the intestine, into Fig. 143. 



which the branched tubes (fig. 143^ o, o ; 

 fig. 142, s) empty themselves. This cir- 

 cumstance has long been a subject of in- 

 teresting inquiry to the comparative phy- 

 siologist. If the fluid secreted by these 

 tubes be really bile, in what manner 

 does it accomplish those purposes usually 

 supposed to be effected by the biliary 

 secretion ? It would seem to be, in this 

 case, merely an excrementitious produc- 

 tion. Are the caeca appended to the 

 stomach biliary organs ? If so, the apparatus in question may be 

 of totally distinct character, and its product only furnished to be 

 expelled from the system. In conformity with the last supposi- 

 tion, many antaomists have been induced to regard these vessels 

 as -being analogous to the urinary secernents of more highly 

 organized animals, and have not scrupled to apply to them the 

 appellation of renal vessels : but this hasty application of names 

 we have already animadverted upon as being highly prejudicial 

 to the interests of science ; and in this instance, as in many others, 

 to wait for the results of future investigations is far more advisable 

 than rashly to assign a definite function to a part, the real nature 

 of which is a matter of speculation. 



(358.) The respiratory system of the Pulmonary Arachnidans is 

 constructed upon very peculiar principles, being neither composed of 

 gills adapted to breathe water, nor lungs like those of other air-breath- 

 ing animals, but presenting a combination of the characters of both. 

 The pulmo-branchite are, in fact, hollow viscera resembling bags ; 

 the walls of which are so folded and arranged in laminae, that a 



