230 bulletin: museum of comparative zoology. 



Without doubt the intercelkilar substance vinder discussion is non- 

 nervous in character. I believe that it is to a large degree composed 

 of cuticular substance which is continuous with the limiting membrane. 

 Whether it contains any material that belongs to the basal cells or not 

 I cannot say. 



V. Nervous Structures. 

 A. In Cristae acusticae. 



The fibres of the ampullar ramuli of the eighth nerve, after pene- 

 trating the basement membrane, pass directly through the zone of 

 supporting cells into what has been called the zone of plexus formation. 

 As will be seen by reference to Figures 12, 14, 16 (Plate 3), it is usual 

 for the coarse, or "giant," fibres to make their way directly to the 

 bases of the cells of the sensory epithelium, where they expand to 

 form the "Kelchbildungen" described by Retzius. My preparations 

 do not justify any such sharp distinction between the giant fibres and 

 the fine fibres as was made by Ramon y Cajal (:04^) in the case of the 

 chick. Such extremes of size exist, but there are, as well, many inter- 

 mediate sizes. 



Besides those fibres which, after penetrating the basement mem- 

 brane, pass directly to the bases of sense cells, there are others of 

 difl^erent sizes, that turn in various directions to supply more remote 

 sense cells. As a consequence there is a stratum between the sup- 

 porting cells and the sensory epithelium in which the axis cylinders are 

 so entangled with one another as to present the appearance of a real 

 network of anastomosing fibres. This has led to the common designa- 

 tion of this stratum as the "zone of plexus formation." Figure 13 

 (Plate 3) represents one of the most complex of such apparent networks 

 afforded by my material. By the use of an oil immersion lens, I 

 found, on careful focusing, that in the great majority of cases the 

 intersecting fibres lie in different focal planes and do not anastomose. 

 I have found some places in which conditions were not sufficiently 

 clear to enable me to decide whether there was anastomosis or not, 

 but I have found no place in which I was certain of anastomosis, and 

 I am satisfied that an interlacing of fibres is the usual condition, and 

 that anastomosis is rare, if indeed it occurs at all. I am therefore 

 inclined to designate this region as the zone of distribution, rather than 

 the zone of plexus formation. 



Very commonly there is, above the zone of distribution, a stratum 



