Literary Notices. cxHx 



nervous system, but forms a peculiarly modified portion of the peri- 

 pheral system. 



The section on the structure of the nerve fibre is quite full and 

 the author retams the old position, that the Schwann's sheath with its 

 corpuscles is derived from connective tissue and has no direct relation 

 with, the formation of the nerve. To the writer, it seems that the 

 evidence from experimental and pathological, as well as histological 

 sources, is overwhelmingly opposed to this view, which rests on un- 

 supported assumption. The above position is the more remarkable in 

 view of the description of the olfactory which follows. The latter, 

 however, simply retains a structure much like that of the earlier stages 

 of all nerves. The section on the spinal cord is practically exhaust- 

 ive. Following the general description of the spinal cord is a com- 

 parative section from which the following data are collected : 



In Amphioxus the cord consists of a folded plate with the edges 

 approximated in such a manner that the ventricle is a mere slit which 

 is clothed with a layer of gray matter composed of epyndyma cells with 

 a few nerve cells. The cell walls of the epyndyma pass from ventri- 

 cle to surface in the form of thin tubes and frequently collect in clus- 

 tres. Aside from these fibres the stroma of the cord is composed of 

 nerve fibres only, there being no neuroglia. In this as well as other 

 respects the cord of Amphioxus resembles the nerve-axis of worms. 

 The nerve fibres are all noii-medullated. Those of the dorsal region 

 are smaller than those of the ventral region and in various regions 

 there appear colossal fibres whose origin can be traced to enormous 

 nerve cells of the dorsal part of the tube. The smallest nerve cells lie 

 with the epyndyma along the ventricle, the intermediate type of cells 

 occurs in a row along either side the ventricle and are bipolar or multi- 

 polar. The colossal cells lie across the ventricle one third its height 

 from the dorsal suface. The cephalic cell of this series lies immedi- 

 ately behind the sixth left sensory root and gives rise to an enormous 

 fibre which lies ventrad of the canal and sends another fibre into the 

 seventh sensory root. Then follow eleven others each of which sends 

 a fibre caudad. From the last of these and the 39th sensory root there 

 are none of the colossal cells, but from that point they reappear and 

 the 14 caudal cells send fibres cephalad. In all cases the colossal 

 fibres cross ventrally to the opposite side before assuming their defini- 

 tive position. The small nerve cells, according to Retzius, send 

 fibres into the sensory roots. ^ 



Of general interest is the suggestion afforded by the relations of 

 the nerve cells that all the nerve cells arise form the epyndyma. 



