MR GOODSIR ON THE ANATOMY OF AMPHIOXUS LANCEOLATUS. 253 



more particularly on the upper surface and groove, is observed to be more abun- 

 dant opposite the origin of the nerves ; and, as it is regularly arranged in this 

 manner in dark masses along the anterior and posterior thirds of the cord, the 

 organ in these places, on superficial inspection, resembles much the abdominal 

 ganglionic cord of an annulose animal. Along the middle third the pigment is 

 not so regular, but appears in spots at short intervals. When any portion of the 

 cord, however, is slightly compressed, and microscopically examined, it becomes 

 evident that there is, along the groove and mesial line of its upper surface, a band, 

 consisting of cells of a larger size than those composing the rest of the organ. 

 Some of these cells only are filled with black pigment, but all of them contain a 

 fluid of a brown tint, which renders the tract of large cells distinctly visible. 

 When the compression is increased the cells burst ; and the fluid which flows from 

 the central tract is seen to contain jet-black granules, which may be detected as 

 they escape from the cells. 



The nerves consist of primitive fibres, of a cylindrical shape, with faint longi- 

 tudinal striae. The primitive fibres of a trunk pass off into a branch, in the usual 

 way, without dividing ; and, where the trunks join the spinal cord, the primitive 

 fibres are seen to approach close to it, but without passing into it. The greater 

 part of the slightly protuberant origin consisting of the nucleated cells of the cord, 

 with a few pigment cells interspersed, the exact mode of termination of the cen- 

 tral extremities of the primitive nervous fibres could not be detected. 



Muscular System. 



This system is highly symmetrical, consisting of a series of lateral muscular 

 bundles, corresponding in number, size, and position, to the vertebrae of the 

 " chorda dorsalis." These bundles have a general resemblance to the division of 

 the lateral muscles of the higher fishes. Each bundle consists of a dorsal and 

 ventral portion. The dorsal passes from the lateral line, on a level with the ver- 

 tebral column, backwards and upwards ; the ventral passes from the same level, 

 downwards and backwards. The inferior bundle is the longest ; and both of them 

 have a somewhat conical shape, and are attached to the spinal column and skin 

 by the aponeurotic septa formerly described. The fibres of these muscles pass 

 respectively from before, obliquely upwards and downwards, almost, but not com- 

 pletely, in the direction of the muscular bundle, along that portion of the trunk 

 occupied by the branchial portion of the intestinal tube. The ventral bundles pass 

 half-way over the dilated cavity, and terminate in blunted extremities, which are 

 attached to the skin, and to the walls of the branchial compartment, so as to dilate 

 it for the reception of sea- water. Beyond the anus the ventral bundles are attached 

 to each side of the fibrous septum above described, meeting below in a sharp ridge. 

 Between the anus and the branchial cavity, where these muscles inclose the diges- 

 tive portion of the intestinal tube, they do not meet completely below, but are 



