THE CRAYFISH. :7 



PLATE IX. 



THE CKAYF1SH. THE GENERAL DISPOSITION OF THE VISCERA. THE ORGANS OF 

 ALIMENTATION, CIRCULATION, AND RESPIRATION. 



FIG. I. A general dissection from the dorsal aspect. 



The whole tergal skeleton has been removed. The extensor-abdominis muscle, the 

 greater part of the generative apparatus, and part of the anterior gastric muscle together 

 with the procephalic process, have been removed on the left side ; the adductor muscle 

 of the mandible has been cut short, and the digestive gland (so-called liver) dissected away 

 to the level of its central duct. 



On the right side the gills were removed, to show the extent of the branchial 

 chamber. <?. x 1. 



FIG. II. The stomach and anterior portion of the intestine, after removal from the 

 body, seen from above. 



The attachments of the gastric muscles (approximators of the gastric teeth) are shown 

 on the left side. 



The whole fore-gut was divested of its outer cellular coat. 



FIG. HI. The same, in median longitudinal section, the wall of the fore-gut being left 

 entire. 



FIG. IV. The terminal portions of the hind-gut and abdomen, in longitudinal 

 section. 



FIG. V. Transverse section of the fore-gut, passing through the oesophagus imme- 

 diately behind the anterior gastric muscle ; a young gastrolith, y., was present. 



The metastoma and basal joint of the first maxilla are drawn in natural position. 



C.T.V. should read bs.v. in this figure. 



In Figs. III. to V. the cut edges of the cuticular lining and its related structures are 

 drawn in black. 



FIG. VI. Outer view of the gastrolith. 



(Figs. II. to VI., all x 2.) 



FIG. VII. Dissection from the left side, to show the leading muscles of the fore-gut, 

 and incidentally in section the labrurn, a portion of the metastoma and the procephalic 

 process. 



The specimen was previously hardened in alcohol. x 1. 



In dissecting the above, the opportunity should not be lost of noting the extent to 

 which the calcifications of the chitinous wall of the stomach are determined by muscular 

 attachment. 



