312 MANUAL OF HISTOLOGY. 



of a non-fibrillated nucleated tissue (fig. 302, A), from which they may 

 be isolated in the form of membraneless corpuscles (B). 



According to recent investigations, the internal surface of each of these 

 corpuscles Fs lined in man and the vertebrate animals with delicate 

 flattened epithelium or endothelium, resembling that of the blood-vessels 

 (Frdntzel, Koelliker, Schwalbe) (1). 



What is the nature of this enveloping nucleated tissue? 



Here we meet with a great variety of opinions. It was formerly set 

 down as being in toto a connective-tissue structure, but Beale and Eemak 

 ascribe to it a nervous character. Be this as it may, the distinct origin 

 of Rematis fibres from these systems of capsules is very remarkable. 



REMARKS. 1. This was noticed years ago by Robin and R. Wagner in the case of 

 the ganglion cells of the electric ray. Heutak too was aware of the presence of this 

 cellular lining. 



178. 



The processes and ramifications of the ganglion cells serve, in the first 

 place, possibly as connections between neighbouring cells (commissural 

 fibres), and, in the next place, they certainly go to form the axis cylinders 

 of different nerve fibres. For the investigation of these very difficult points 

 the lower orders of vertebrates, and especially fishes, are to be recom- 

 mended, in which the dissection is rendered easy by the small amount of 

 enveloping connective- tissue (1). The following points may be noticed 

 in the nervous knots of the burbot \_Gadus lota (2) ] (fig. 304). 



Some of the ganglion cells appear apolar (i, &), no trace even of 

 ruptured processes being discoverable, the appearance of the capsule 

 conveying the impression rather of its being closed. These represent 

 possibly only the earlier stages of development of ramifying cells (Beale). 



Others, and they are of a smaller kind, are unipolar, giving off at one 

 end a process which assumes, after having run for a certain distance, a 

 darker and more medullated appearance, becoming eventually a narrow 

 nerve fibre (/). On some ganglion cells, though apparently unipolar (e), 

 another ruptured portion of fibre may be recognised on the mutilated 

 envelope. Unipolar cells, continuous through their processes with broad 

 nerve tubes, are not met with. 



Bipolar ganglion cells are of frequent occurrence. The smaller are in 

 communication with narrow, the larger with broad, nerve fibres. The 

 first (d) frequently show us pale fibres of considerable length, which, 

 in the case of the unipolar cell, become transformed into nerve tubes. 

 The latter (a, b, c) present to us the fibre as a dark medullated tube, 

 extending as far as the extremity of the cell (a). Here the medullary 

 matter spreads out in a thin layer, investing the body of the latter (3) 

 and may persist in that situation even after the rest *of it has escaped 

 from the cut end of the nervous tube (5, c). 



Such bipolar origins as at h are of rare occurrence, as also the appear- 

 ance of two ganglion cells on one and the same nervous tube, as at g. 



Our diagrams show also that the enveloping neurilemma or capsule of 

 the ganglion cell is continuous with the connective-tissue primitive sheath 

 of the nerve tube. In the peripheral ganglia of fishes, multipolar cells 

 do not occur. Even those with three processes, are very rare (Stannius). 



The recognition of corresponding structural relations in the human 

 being and among the mammalia is of much greater difficulty, owing to 

 the larger proportion of interstitial connective- tissue, and mutilated 



