ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 627 



like organs of C. Stewart. Of the four kinds of pedicellariai in 

 Schizaster canaliferus one is tetradactyle ; in this form there are only 

 two pairs of genital glands, and the sand canal does not follow its 

 usual complicated course. In Brissoj)sis lyrifera the author notes a 

 narrow canal which he looks upon as being a second " siphon," and, 

 in conclusion, he states that while his observations have led him to 

 see only slight modifications in the details of the anatomical structure 

 and arraugements of the internal organs of regular Echinoids, he 

 finds tbat in the irregular forms the internal organs have, in their 

 differentiation, followed the migrations of the branches, which com- 

 menced in the Jurassic period and appear to have profoundly affected 

 their primitive structure. 



Anatomy of Spatangus purpureus.* — E. Koehler has studied the 

 circulatory system of this Echinoid. He finds that the branch de- 

 scribed by Hoffmann, connecting the intestinal vessel with the 

 perioral ring, bifurcates at the level of the mouth, and sends one 

 branch to the blood-vascular ring and the other to the ambulacral 

 ring. The sand- canal is double between the mouth and the end of 

 the oesophagus ; it remains single from this point up to the second 

 curvature of tbe alimentary canal, and after this is divided by septa into 

 several secondary chambers, up to the point where it opens into the 

 " heart " ; on the opposite side of that organ it becomes a narrow 

 tube. The so-called heart is spongy, and its cavity is in direct con- 

 nection with that of the sand-canal ; it consists of connective tissue, 

 provided with numerous nuclei and cellular elements resembling 

 those of the blood ; the membrane which attaches the sand-canal to 

 the madreporic tubercle has a similar structure, and perhaps both 

 organs are glandular, and discharge either excretory or blood- vascular 

 functions. The blood-vessels of the alimentary canal are derived 

 from the external and internal marginal trunks, but the oesophagus, 

 the 3rd curvature, and the rectum, are quite devoid of vessels. Most of 

 those on the 2nd curvature occur on its dorsal surface, the only ventral 

 vessels in this region being found near the orifice and on each side of the 

 diverticulum. The intestinal vessel of Hoffmann does not reach the 

 stomach. The vessels of the latter consist of a very close plexus 

 formed around the opening of the diverticulum by the two marginal 

 vessels and of vessels derived from this plexus, and extending along 

 each side of the stomach as far as the siphon and connected by trans- 

 verse tubes both on the anterior and posterior sides. The right- 

 hand branch sends twigs to the mesentery between the diverticulum 

 and alimentary canal. All these branches re-unite into a trunk 

 which follows the course of the diverticulum up to the heart. 



Over the vascular parts of the digestive canal the epithelium is 

 thicker and composed of larger and longer cells than the non-vascular 

 parts. This epithelium is made up of several layers of cells, the 

 deepest being rounded, small, closely appressed, tho superficial ones 

 very long, 10 or 15 diameters in length; below it is a delicate continuous 

 elastic membrane. The connective tissue behind the membrane forms 



* Comptes Kcndus, xciii. (1SS1) pp. 651-3; xriv.. pp. 139-11. 



