Common Crayjish. 103 



rostrum. Between these gastric muscles anteriorly is seen the 

 azygos stomato-g-astric nerve entering a small ganglion. From 

 this gang-lion it is continued onwards, after giving off a nerve on 

 either side, across the cardiac ossicle, posteriorly to which it bifur- 

 cates, and joins one of the lateral storaato-gastric nerves to supply 

 the liver lobes. A small ossicle, the ' pterocardiac,' articulates 

 with either outer angle of the cardiac ; and from the base thus 

 constituted the supero-lateral ossicles pass backwards so as to form 

 with it anteriorly, and with the ' pyloric ossicle^ distally, a tri- 

 angular framework, into the apex of which two other muscles are 

 inserted, which take origin posteriorly from the carapace. Imme- 

 diately in apposition with the portion of the stomach thus strength- 

 ened, is seen the end of the adductor mandibulae muscle, separated 

 from its attachment to the carajjace ; and exteriorly again to the 

 muscle, are seen on either side the two lobes of the liver. In the 

 middle line between the hepatic lobes are seen the paii'ed lobes of 

 the testis. Where these lobes join an azygos lobe placed pos- 

 teriorly to them in the middle line, and superiorly to the in- 

 testine, the vasa deferentia are seen taking origin as slender tubes, 

 the caliln-e of which rapidly widens, and the lengthy convolutions 

 formed by which intrude some way into the post-abdominal cavity, 

 before they turn downwards to open in the basal joint of the last 

 abdominal limb on either side. Posteriorly, the comparatively 

 small strata of extensor muscles having been removed, we see the 

 intestine taking- a straight course, as always in Crustacea, to the 

 anus. Externally to the vasa deferentia and hepatic lobes are seen 

 the branchial organs, arranged in three rows, the outermost con- 

 sisting of the branchiferous ejiipodites, which are develo])ed upon 

 the coxopodites of the two posterior maxillipeds and upon the four 

 anterior ambulatory legs ; and the two innermost of simple tree-like 

 upgrowths, developed in pairs from the third maxilliped to the 

 fourth ambulatory leg inclusively, and singly u])on the second 

 maxilliped and the last ambulatory leg. The branchiferous epipo- 

 dites are in shape like a leaf, with the two halves of the blade or 

 lamina folded backwards, and with the mid-rib looking forwards. 

 Both halves arc longitudinally plicated, but the branchial lilanients 

 are developed only upon the half which looks outwards. The bi-an- 

 chiae proper are sessile, internally to the epi})oditcs, upon the cpimera, 

 and the membrane intervening between them and the basal joints 



