608 p. HERBERT CARPENTER. 



disappears, and these two canals pass up side by side towards 

 the apical pole. 



The results of Koehler's injections lead him to identify the 

 second canal with one or two canals which pass from the sur- 

 face of the gland on to its supporting mesentery, where they 

 lose themselves in a large and irregular network in the inter- 

 stices of the connective tissue. According to Koehler, there- 

 fore, the two vessels which together make up the stone-canal 

 at the level of the gullet, each communicating with one of the 

 peribuccal rings, soon fuse into a single canal that terminates 

 in a gland placed at the extremity of the diverticulum, while 

 the intestinal vessel communicates through its connecting 

 branch with both the peribuccal rings. " The fusion of the 

 two systems is thus as complete as possible, and it would be 

 difficult to admit the existence of a distinction between a 

 water-vascular and a blood- vascular system. 



To this I would remark : (1) The fact that each peribuccal 

 rino- sends a separate branch into the ambulacra, does not 

 look like a more complete fusion of the two systems than exists 

 in Echinus; where Koehler, though I believe wrongly, des- 

 cribes both the radial vessels as communicating only with the 

 water-vascular ring. He cannot surely mean that each ring 

 in Spatangus communicates with both the radial vessels. 

 As regards the connecting branch joining both the peribuccal 

 rings, I should wish, as I have pointed out above, for more 

 distinct proof than a mere assertion. 



(2) Koehler regards the organ which is commonly called the 

 stone-canal of Spatangus, as homologous with the glandular 

 canal of Echinus, on account of its relations to the excretory 

 gland. It appears to me, however, that Teuscher's identifi- 

 cation of the canal with columnar epithelium, found by him at 

 the apical pole, as the water- tube, is more correct than 

 Koehler's view of what is evidently the same structure. A 

 canal of this kind would not be likely to end in a vascular 

 network in the mesentery; and I cannot but think that 

 Koehler, who does not mention Teuscher^s opinion, is here 

 in error. Both authors agree in its peripheral position as 



