374 



THE ORIGIN OF VERTEBRATES 



lie describes them simply as conical eminences, and states that they 

 " recouvrent nn pore analogue a celni des poils mais plus petit ; 

 il est rempli par le protoplasma de la conche hypodermiqne." 

 From the ganglion, according to him, nervous prolongations pass, 

 which traverse the chitinogenous layer and terminate at the base 

 of the conical eminences. Each of these prolongations " presente 

 sur son trajet, mais im peu plus pres du ganglion que de sa termi- 

 naison peripherique, une cellule nerveuse fusiforme (g.) offrant, 

 comme celles du ganglion, un gros noyau." He illustrates his 



description with the following, Fig. 153, 

 taken from his paper. 



I have not been able to obtain any evi- 

 dence of a fusiform nerve-cell on the course 

 of the terminal nerve-fibres as depicted by 

 him ; fusiform cells there are in plenty, as 

 depicted in my drawing, but none with a 

 large nucleus resembling those of the main 

 ganglion. In no case, either in the flabellum 

 or in the branchial organs of Limulus, or in 

 the pecten-organs, have I ever seen a ganglion- 

 cell within the chitin-layer ; all the nuclei 

 seen there resemble those of the cells of 

 the hypodermis or else the elongated nuclei 

 characteristic of the presence of nerve-fibres. 

 Gaubert's drawing is a striking one, and I 

 have looked through my specimens to see 

 whether there was anything similar, but have 

 ?*., nerve; gl., ganglion. hitherto failed to obtain any definite evidence 



of anything of the kind. 

 I feel, myself, that an exhaustive examination of the structure 

 and function of the pecten of scorpions ought to be undertaken. At 

 present I can only draw the attention of my readers to the similarity 

 of the arrangement of parts, and of the nature of the end-organs, in 

 the sense-organs of the flabellum of Limulus and of the pecten of 

 the scorpion. In both cases the special nerve-fibres terminate in 

 a massive ganglion, situated just below the chitinogenous layer. In 

 both cases the terminal fibres from these ganglion-cells pass through 

 the modified chitinous layer to supply end-organs of a striking cha- 

 racter ; and although the end-organ of the pecten of the scorpion does 



Fig. 153 (from Gaubert). 

 — Section op a Tooth 

 of Pecten of Scorpion. 



