144 McMURRrCH. [Vol. IV. 



glion cells, but there is certainly no such development of ganglion 

 cells as Danielssen describes as occurring in his C. borealis. 



This description agrees essentially with that of the Hertwigs. 

 It is well known, however, that von Heider's observations 

 differ somewhat from those of the Hertwigs. He describes as 

 occurring in the lower part of the epithelial layer an " Inter- 

 basalnetz " of fibres, formed by the anastomosis of fine branch- 

 ing processes of the epithelial cells. In the meshes of the 

 network are fine, sharply outlined points, which are supposed to 

 be cross-sections of delicate fibrils. These fibrils are nervous, 

 and send branches upwards to the epithelial cells, and down- 

 wards to the mesogloea. The Hertwigs, in discussing in an 

 appendix von Heider's results, identify this " Interbasalsub- 

 stanz " with their nerve band. This, however, is a mistake. In 

 all sections taken from one of my specimens I get an appear- 

 ance similar to that shown in the Hertwigs' PI. VIII., Fig. ii ; 

 in all the sections taken from another specimen. I get von 

 Heider's " Interbasalnetz." Why there is this difference in 

 the two specimens I cannot say. It may be due to a difference 

 in the amount of contraction. The nerve band in those prepa- 

 rations which show the " Interbasalnetz " is plainly visible, 

 lying between the muscle layer and the network, and corre- 

 sponding therefore with the fibrillar layer which von Heider 

 describes as appertaining to the "mesoderm," which is shown 

 in his PI. v., Fig. 35, /. It is this fibrillar layer then, and 

 not the " Interbasalnetz," which is the nerve band. It is 

 possible that the " Interbasalnetz" appearance may be produced 

 by the great contraction of the mesogloea and of its processes, 

 which extend up into the epithelial layer. This idea is 

 strengthened by the fact that gland cells and nematocysts are 

 of very frequent occurrence in the network, — a fact that shows 

 that it belongs to the epithelial layer. 



The longitudinal musculature of the column is as usual well 

 developed. For some distance below the margin it is no higher 

 than the musculature of the disc, but lower down it increases 

 in size, reaching its greatest height about the middle of the 

 column, where it is many times higher than on the disc. This 

 height it retains almost unaltered to within at least 2 mm. of the 

 posterior extremity, except along the dorsal median line, where 

 it is throughout low as in C. vicmbranaceus. It has essentially 



