264 Journal of Comparative Neurology. 



2. TJie segmental afferejit neuroties. The cells of origin 

 of the afferent neurones are grouped together in the spinal 

 ganglia and the ganglia of the afferent cranial nerves. The 

 olfactory afferent neurones belong to the type described as 

 modified epithelial cells (see the description of the nervous sys- 

 tem of Lumbricus) ; in the Amphioxus there is a third type in- 

 asmuch as the sensory neurones have their cell-bodies within 

 the spinal cord. It is possible that the midbrain-root of the 

 fifth nerve belongs to this category. Both these types can- 

 not come into question in this general study. 



Since Flemming gave his classical description of the spinal 

 ganglion cell, many important studies have come forth. Espec- 

 ially the important experiments of Hodge were made on them; 

 further we have detailed descriptions by v. Lenhossek, Held 

 and Nissl. We start with the description of the cell-body as it 

 presents itself with the Nissl method. The cells of this type 

 (see the drawing by Nissl, Neurolog. Centralblatt, 1894, and 

 also the plates of v. Lenhossek, Archiv fiir Psychiatrie, Vol. 

 29, Taf. VI and VII) are round or oval, with only one nerve- 

 process in the human adult, but two in the embryo. The nu- 

 cleus is located near the center, with a plain membrane and 

 moderately large nucleolus. The stainable substance consists 

 of smaller lumps than in the motor cells ; they vary greatly in 

 size and distribution, so that Nissl is obliged to describe several 

 ' equivalents ' or types. The larger particles are usually con- 

 centrically arranged either close to the periphery or further to- 

 wards the nucleus in one or more Mayers;' smaller particles 

 give a less clearly concentric arrangement. The larger particles 

 appear usually composed of smaller ones and are not homoge- 

 neous. The non-stainable substance is also more or less con- 

 centrically arranged but not in as plain paths as in the motor 

 neurones ; in many cells there is a superficial layer quite free of 

 stainable substance. Where the axone arises there is a plain 

 cone of origin, free of stainable substance. 



The principal discussion has turned around the char- 

 acter of the non-stainable substance. Held and Lenhossek 

 (quite recently, however, Lenhossek has expressed himself in a 



