626 EXCRETING ORGANS. 



trunk, have obvious affinities, both to urinary and branchial 

 organs, and may perform the function of both these great 

 emunctories. Distinct isolated follicles, (Fig. 1 14. z.), however, 

 more resembling simple urinary tubuli, are already perceptible 

 in this animal, developed from the cloacal end of these large or- 

 gans, and to which the urinary function may be confined. The 

 calciferous gland of the asterias may have a similar function. 

 Although numerous salivary, mucous, and biliary 

 follicles pour their secretions, partly excrementitious, into 

 the alimentary canal in the helminthoid animals, no distinct 

 formation of uric or lithic acid has hitherto indicated a 

 urinary function in any of these simple glands. Among the 

 entomoid articulata, many insects and arachnida exhibit, 

 besides the ordinary biliary tubes opening into the higher 

 chylific portion of the alimentary canal, distinct small 

 secreting follicles or tubuli developed from the lower ex- 

 cretory part of the intestine, like the renal organs of verte- 

 brated animals, and these structural analogies have been 

 confirmed by their chemical products, by the uric and lithic 

 acids discovered in their secretions. These simple tubuli 

 uriniferi pour their secretion into the cloacal part of the 

 intestine near the anus, and in some of the coleopterous 

 insects, as in ditiscus, there is a distinct small vesicle or 

 urinary bladder into which one or two renal tubes convey 

 their secretion, before opening into the terminal part of the 

 intestine. The renal tubuli were pointed out by Treviranus 

 in the iulus among the myriapods, they have been detected 

 in some of the Crustacea, as the pagurus, and they are seen 

 in the spiders among the arachnida. The urinary organs, 

 like other glands of mollusca, have seldom the form of 

 elongated isolated tubuli, as they have in the articulated 

 tribes, but generally present the form of short wide secreting 

 sacs, opening near the anus or the genital organs. Such 

 sacs are seen in many conchiferous mollusca, situate in the 

 dorsal part of the body below the heart, and opening by 

 two short ducts along with the oviducts, near the anus ; 

 these are often charged with earthy particles, and have been 

 generally considered as destined to secrete the calcareous 

 nratter of the valves. In several of the terrestrial and fresh- 

 water gasteropods breathing atmospheric air by pulmonary 

 sacs, uric acid has been detected in the secretion of a small 

 excretory gland, laminated internally, filled with solid 



