Commo7i Crayjish. 99 



the intestine; a third is placed underneath the sternal artery ^ just 

 at its origin from the bulbus arteriosus, at the posterior extremity 

 of the heart_, from which the post-abdominal artery just mentioned 

 is continued directly backwards; the fourth and most anteriorly 

 placed slip of blue paper occupies an interval between the coecal 

 process, the rudiment of the embryonic yelk-sac, which marks the 

 commencement of the intestine, and the hepatic artery of the left 

 side, just as it emerges from under the cover of the testis, and 

 passes down on to the pylorus. The anterior wall of the stomach, 

 finally, has been displaced a little backwards, and the commissural 

 cord between the supra- and the infra-oesophageal ganglia, which 

 was rendered visible by the removal of the antennary gland, has 

 had its various connections made more evident. 



The twelve post-oral and the supra-oesophageal ganglia are here 

 seen in profile, and the great lengths of the commissural cords 

 passing between the last-named ganglia and the first of the post- 

 oral series whence the three pairs of foot-jaws as well as the three 

 pairs of true jaws are supplied, is well seen, corresponding with the 

 elongated antennary sternum. Visceral nerves are seen passing 

 from the commissural cords and from the supra-oesophageal mass 

 on to the stomach. A sub-circular raised area on the anterior 

 aspect of the stomach as displaced backwards, and about midway 

 between its upper and lower border, marks the position of the 

 so-called ' eye/ a circular calcareous disc periodically developed in 

 the Crayfish. A convex protuberance marks the pylorus, imme- 

 diately behind which is seen, the two hepatic lobes having been 

 cut away, the opening of the left ductus eholedochus into the 

 commencement of the intestine. The inferior portions of the 

 hepatic lobes of the right side come into view beneath the pyloric 

 portion of the stomach and the duodenum, along the middle line of 

 which they come into the apposition with the homologous portions 

 of the left hepatic lobes. The convolutions of the vas deferens 

 of the left side fill up the space between the two slips of blue 

 paper which are placed under the hepatic and the sternal arteries, 

 and which abut by their upper angles upon the anterior paired 

 and the posterior azygos testicular lobe respectively. Superiorly 

 to the testicular lobes, and, as in all Arthropoda which possess 

 it, immediately underneath the dorsal integument, is seen the 

 heart. In the interior of the post-abdominal region are seen, 



II 2 



