152 Miscellaneous. 



the nerves; this I have been able to coulinn. He has, however, 

 left us in doubt as to the origin of the nerves ; and with regard to 

 their terminations his observations are very imperfect, which I at- 

 tribute to the inferiority of the microscopes of 1844 as compared 

 with those of 1862. 



The central nervous system consists of cells and fibres. The cells 

 are very delicate, transparent, round, and filled with granulations, 

 and their diameter is from 0*02 to 0*05 mill. ; their little nucleus is 

 only 0"006 mill, in diameter. In the living animal I could not 

 ascertain their presence ; and I could only see them after j)lacing the 

 whole animal in a weak solution of chromic acid. The sheath of 

 the central nervous system, discovered by Quatrefages, exists ; but 

 the nervous fibres, denied by him, also exist ; they are very deli- 

 cate, straight, and covered with small granulations. 



Besides these two elements, there is a great quantity of capillaries 

 in the central nervous system. Quatrefages discovered " that beyond 

 the last inflation the medulla spinalis is produced into a delicate fila- 

 ment, which becomes dilated and forms a sort of very distinct am- 

 pulla on the level of the extremity of the dorsal chord." The ob- 

 servation is correct ; but the ampulla and the whole of this terminal 

 filament are nothing but caj/illaries, a loop of which forms the 

 ampulla. 



The spinal nerves spring from the upper part of the sides of the 

 medulla spinalis, as I saw in transverse sections. From this the 

 roots start in the form of a comparatively thick trunk. There are 

 not two roots ; but in the interior of the root we find very delicate 

 primitive fibres (cylindraxes), which reach it from different sides. 

 The roots are surrounded by a sheath, in which capillaries may be 

 detected. After its issue the nervous trunk becomes swelled ; and I 

 once succeeded in seeing in this swelling a ganglionic cell with its 

 nucleus. It is only behind the swelling that the trunk divides, as 

 described by Miiller and Quatrefages. L believe that the swelling 

 represents the spinal ganglion of the vertebrata. 



Termination of the Nerves. — Of this, Quatrefages saw two modes : 

 in one he saw and depicted a nervous filament, "terminating in some 

 small ovoid vesicular organs, with proportionally thick walls, which 

 are probably muciparous crypts ;" in the other he saw the nerves 

 terminate in transparent homogeneous filaments, which at their very 

 extremity " spread out to form an irregular cone, or a small ma- 

 milla applied against the inner layer of the integuments." The 

 structures described by Quatrefages exist, but he observed only the 

 beginning of the end. The little vesicular organs do not constitute 

 a termination, but they are placed in the course of the last ramifica- 

 tions of the nerves. There are two kinds of these bodies— large and 

 small. It is especially in the upper part of the head that I have 

 seen them ; in the lower part and in the margin of the fin they are 

 much fewer. But these bodies, which at the first glance have the 

 form of a nucleated cell, are only loops of the nervous fibre ; that 

 IS to say, the fibre, instead of running straight onwards, turns round 

 upon Itself. Sometimes the arrangement is repeated, so that the 



