ON THE BRITISH EDRIOPHTHALMA. 49 



verges and unites with the alimentary canal, on the inferior surface, it is 

 united with the liver. 



From the stomach, the alimentary tube is continued in a direct line to 

 the anal extremity. To this general law we know of but one exception, and 

 that upon the authority of Professor Allman, who states that in Chelura 

 terebrans the alimentary canal is so arranged as to shut one part within 

 another to admit of the head being projected forwards, that the animal may 

 eat its way into the wood. 



In a few species the alimentary tube is continued beyond the posterior 

 limits of the calcareous tissue of the animal, and is furnished with a slightly 

 pectinated edge. 



The most constant condition is, that the anus shall coterminate with the 

 last segment, and is there closed by a set of transverse muscles which pro- 

 bably fultil the office of a sphincter (PI. XX. fig. 1 c). 



The structure of the walls of the canal appears to be a membrane pos- 

 sessing a fibrous character which stripes it in a longitudinal direction (PI. XIX, 

 fig. 5). Transverse lines of a finer appearance are also perceptible (fig. 6) ; 

 and the general appearance of the whole is that of a passage surrounded 

 with elastic walb. 



The stomach is retained in its position ; first, by being supported upon flat 

 calcareous plates (PI. XII. figs. 4 O & 5), processes of the dorsal part of the 

 segment which carries the maxillae. These processes are flattened to receive 

 the organ, which is further retained in its position by a calcareous con- 

 tinuation on each side. Besides, there are several muscles, some of which 

 are attached to the upper external surface and retain it anteriorly, while 

 others are attached to the under surface and hold it posteriorly in position 

 (PI. XIX. fig. 2,/ &^). 



The Liver appears to be among the most important of the viscera, if we 

 may judge from its relative size. It uniformly, as far as our experience 

 teaches us, consists of four long simple sacs filled with biliary cells, the 

 contents of which are yellow in colour (PI. XIX. figs. 3 p). These separate 

 sacs unite together at their anterior extremity into a single short biliary 

 duct, which opens into the intestinal tube on the under aspect, immediately 

 where it leaves the stomach. 



Urinary organs. — About two-thirds the distance from the stomach to the 

 anal aperture, two long cylindrical appendages, closed at the free extremity, 

 communicate laterally upon the upper side with the intestinal tube (PI. XX. 

 fig. 2). These appendages are more important in appearance in some 

 species of Amphipoda. than in others ; but as far as our experience guides, 

 they are universally present both in male and female, as also in the imma- 

 ture animal. In the younger forms they are rudimentary, as shown in fig. 4, 

 taken fvom Amphitoii ; but are scarcely more so than those found in the adult 

 Gammarus grossimanus, as shown in fig. 3 of the same Plate. 



Immediately posterior to the communication of this organ with the ali- 

 mentary canal are a series of muscular fibres transversely lying across the 

 latter (PI. XIX. fig. 1 J) ; they strongly assimilate both in form and arrange- 

 ment with those which we have already mentioned as being sphincter muscles, 

 to the terminal orifice ,of the alimentary tube. The position which this 

 second set of muscles holds is at the immediate point of communication 

 between the two organs, and the general appearance would also induce us to 

 believe that their object is to fulfil a similar office and keep compressed the 

 efi'erent orifice. In fact they act the part of sphincter muscles to the 

 urinary organ. 



Although we name these the urinary organs, yet it is without perfect 

 1855. " E 



