550 John Beard 



and thickly packed. The ganglion cells {ff.c) are large , with larga 

 nucleus and deeply stainìng nueleolus. They are few in number , never 

 more than six or eìght being seen in one transverse section. 



They possess an imdetermined number of proeesses which end in 

 nerve fibres. These ganglionic cells seem to be confined to the portion 

 of the nervous system from which nerves, and especially large nerves 

 are given off. We bave indeed in their arrangement traces of a series 

 of ganglia , which however by degeneration bave lost their primitive 

 character of segmentai ganglia. 



The whole nervous system is enclosed by a layer of connective 

 tissue , and lies in the connective tissue under the alimentary canal 

 (fig. 37 and 38). 



With regard to the number of nerves, their course etc. described by 

 Prof. Graff S I bave nothing new to add, and can only say that I bave 

 failed entirely to find any oesophageal collar. If such a collar existed, 

 and especially if it had the form and relative size fìgured by Graff in 

 Piate XI fig. 8, it could hardly escape being seen in sections. Prof. 

 Graff only found it once in M. citriferum, and then under the dissect- 

 ing microscope. In spite of ali a priori probabilities and ali possibili- 

 ties of its presence I caunot but think that at present the evidence is a 

 little uncertain. 



Against a priori reasoning in favour of its presence it may be urged 

 that Myzostoma has no head and no head sense organs, hence can bave 

 no use for a supra-oesophageal gangliou and nerve collar or for either. 

 The rest of the nervous system , which chiefly supplies muscles , in 

 spite of its size. is not very highly developed. Indeed the whole con- 

 dition of the nervous system points to degeneration. 



Alimentary Canal. 



A few words as to the character of the epithelium in different por- 

 tion of the canal. The epithelium is cylindrical throughout , but on the 

 dorsal side of the stomach it is not so high as and more square than 

 on the ventral (tìg. 35). This condition is reversed in the intestine, 

 there it is the ventral portion which is flattened while the dorsal portion 

 is composed of long narrow cells (figs. 37 and 38). 



» 1. e. p. 56. 



