220 REPORT— 1851. 



an opening considerably more contracted in diameter tlian that portion of 

 the intestine from which it leads. Thus the intestine of the Errant Annelids 

 especially, may be aptly compared to a line of pears, the apex of each suc- 

 cessive pear being applied to the base of its predecessor in the series. If 

 these ' bases ' were prolonged on each side, the stomach of the leech would 

 result; if compressed, that of those species in which the tube is nearly 

 straight. The membranous bridles tying the intestine to the integument 

 are endowed with contractile muscular property, minute fascicles of muscu- 

 lar fibre being detectable amidst the elastic fibres which form the bulk of the 

 structure. In nearly all Annelids the alimentary tube is provided with two 

 distinct orifices. An exception to this rule occurs in the instance of the 

 Planarian family, in which the digestive apparatus is constructed on the 

 type of that of the Radiata. There exist other minor families of Annelids 

 in which the terminal outlet of the alimentary system is not seated at the 

 extreme end of the body, but at a point, at the side, more or less removed 

 backwards from the head, resembling intimately the pattern on which that 

 of the Sipunculidce is formed. These varieties will be afterwards studied in 

 detail. 



The digestive apparatus of the Annelid, considered as a whole, admits of 

 subdivision essentially only into two portions, distinct alike in structure and 

 function. The first would comprehend the proboscis and oesophagus, the 

 second the glandular portion of the canal. The proboscis is no other than 

 a modification of the oesophagus. It is analogous to the latter in structure 

 and uses. It is not always a merely prehensile instrument. Its parietes are 

 beset in many species with glands which contribute a salivary secretion. 

 The jaws are only evolutions of the epithelial layer. The proboscis is to 

 the worm what the whole buccal apparatus is to the mammal. The true 

 oesophagus is essentially a muscular tube, in some species capable of ex- 

 traordinary elongation, and destined only to convey the food from the mouth 

 to the glandular segment of the digestive canal. 



On the parietes of the glandular or intestinal segment only one class of 

 glands is distinguishable. From various considerations, it cannot be doubted 

 that this forms the true biliary system of the Annelid. These glands, viewed 

 collectively, constitute a layer, more or less thick, almost always brilliantly 

 yellow, embracing, like a membrane, the whole cylinder of the intestine. A 

 separate glandule consists only of a minute bag, communicating by a separate 

 opening with the intestine, and filled with oil-molecules of a bright yellow 

 colour. These glandules become, as the posterior extremity of the canal is 

 approached, separated from each other by a more and more sensible interval, 

 enabling the eye to resolve them into their true elementary structure. Esti- 

 mated then by the evidence derived from anatomy, the zoo- chemist would 

 recognise only two classes of secretions in the digestive processes of the 

 Annelid ; first the salivary, and secondly the biliary. It is not without strong 

 reasons that the inquiry may be here suggested, whether a given secretion, 

 although physiologically identical in different orders of animals, is on that 

 account chemically identical. A secretion may be entitled to be called ' bile,' 

 and the organ secreting it may, in all cases, with strict anatomical propriety, 

 be called the liver, and yet the secretion, in ultimate analysis, may present 

 the most striking diversities. According to the most recent researches of 

 Strecker, for instance, the bile of diff'erent animals is found to contain dif- 

 ferent proportions of alkaline taurocholates and glycocholates. In the bile 

 of fishes the resinoid constituents consist almost entirely of taurocholates, 

 with mere traces only of glycocholates. In the bile of dogs scarcely any- 

 thing but taurocholate of soda is discovered ; and the same remark applies 



