ALIMENTARY CANAL. 45 



the genera, except in Alepas, in which they are transverse 

 and reticulated : the whole stomach is thus coated. There 

 is, also, a coating of excessively delicate, longitudinal and 

 transverse muscles without striae. The rectum varies in 

 length, extending inwards from the anus to between the 

 bases of the second and fifth pair of cirri : it is narrow, 

 and formed of much folded transparent membrane, re- 

 sembling the oesophagus, continuous with the outer 

 integuments, with which it is periodically moulted. The 

 anus is a small longitudinal slit, in the triangular piece of 

 membrane representing the abdomen, let in between the 

 last thoracic tergal arches, as already mentioned under the 

 head of the Metamorphoses ; it lies almost between the 

 caudal appendages, and opens on the dorsal surface. 

 Within the stomach, there can generally be plainly seen, 

 in accordance with the period of digestion when the speci- 

 men was taken, a thin, yet strong, perfectly transparent 

 epithelial membrane, not exhibiting under the highest 

 power of the microscope any structure : it enters the 

 branching caeca, and extends from the edge of the bell 

 of the oesophagus to the commencement of the closed 

 rectum, and consequently terminates in a point : it con- 

 sists of chitine, like the outer integuments of the animal, 

 and by placing the whole body in caustic potash, I have 

 dissolved the outer coats of the stomach, and seen the 

 bag open at its upper end, perfectly preserved, floating 

 in the middle of the body, and full of the debris of the 

 food. In most of the specimens which I have examined, 

 preserved in spirits of wine, this epithelial lining was some 

 little way distant and separate from the coats of the 

 stomach ; and hence was thought by M. Martin St. Ange 

 to be a distinct organ, like the closed tube in certain 

 Annelids. Occasionally, I have seen one imperfect epi- 

 thelial bag or tube within another and later-formed one. 

 Digestion seems to go on at the same rate throughout the 

 whole length of the stomach ; if there be any difference, 

 the least digested portions lie in the lower and narrower 

 part. The prey, consisting generally of Crustacea, infu- 



