NERVOUS SYSTEM. PROTOOHORDATA. 63 



passes without being implicated in the ganglion, through 

 the substance of the mantle to the muscle-fibres of the 

 lateral fin, is indicated by a black bristle. 0. C. 1307. 



Hunterian. 



PROTOCHORDATA. 



TTOICATA. 



D. 65. A Simple Ascidian (Phallusia mammillata) from which 

 the dorsal parts of the test have been removed to show 

 the nervous system. In the adult this is in a much 

 reduced condition ; it is minute compared with the bulk of 

 the animal, and consists of a rod-like ganglion that lies on 

 the muscular body- wall upon the dorsal surface between the 

 oral and atrial apertures, close in front of the latter. From 

 either end it gives off a pair of nerves that respectively 

 innervate the integument and muscles of the oral and atrial 

 siphons. A few small nerves for the general body-wall 

 arise from its lateral parts. The hinder end of the ganglion 

 is prolonged backwards as a fine ganglionic cord, that runs 

 along the dorsal edge of the branchial sac and terminates 

 upon the liver. This cord (visceral cord) apparently inner- 

 vates the anterior region of the alimentary canal ; it has 

 been shown to be the degenerate remains of the portion of 

 the larval dorsal cord that lies between the cerebral vesicle 

 and the tail. 0. C. 1307 A. 



Presented by Prof. C. Stewart. 



Van Beneden & Julin, Arch, de Biol., t. v. 1884, pp. 317 

 &633. 



CEPHALOCHOKDA. 



D. 66. The isolated central nervous system of a Lancelet 

 (Amphioxus lanceolatus) showing its general form and 

 some few of the spinal nerve roots. The central nervous 

 system in Amphioxus consists of an unsegmented tubular 

 cord of roughly triangular cross section. At either end it 

 narrows to a point, but otherwise is of approximately 

 similar calibre throughout. It lies upon the dorsal surface 

 of the notochord, extending from its hinder extremity to a 

 point some little distance behind its anterior end. The 



