390 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



fibres of the cephalic region, besides the sheath-proper of the ganglia. The inferior 

 commissure, often of a deep red hue, is well marked, and placed quite at the 

 front. The anterior curves of the ganglia do not bulge so much forwards on each 

 side as in Ommatoplea, and thus the anterior margin of the system forms a 

 nearly uniform transverse line. The superior commissure is smaller and less 

 distinct ; indeed, it is with difficulty seen in the living animal as a transparent 

 preparation. Each ganglion is composed of a superior and an inferior lobe; and 

 in minute structure of the nervous matter agrees with that in Ommatoplea. On 

 making a transverse section through the ganglionic mass just behind the com- 

 missure, the superior lobe is found to be more rounded than the inferior, and 

 to communicate with its fellow of the opposite side by the superior commissure. 

 The inferior is somewhat ovoid, and the great commissure joins it with its fellow ; 

 while posteriorly each gives off the great nerve-trunk. In front the two lobes 

 are soldered together, but towards the posterior part a section is now and then 

 found, which shows the posterior end of the upper lobe separated from the 

 inferior. This severing of the end of the upper lobe is not to be confounded with 

 the free rounded sac which lies close behind, as demonstrated in a section in 

 which the knife has cut the left ganglion somewhat further back than the 

 right, and so indicated this separation on that side. The presence of the trumpet- 

 shaped mouths of the ducts of the cephalic sacs in such a section shows that 

 these bodies are posterior and not yet reached by the instrument. Longitudinal 

 sections of the head of the worm exhibit the positions of the ganglia and the 

 cephalic sacs with great clearness, each of the former often presenting different 

 appearances on the respective sides from obliquity of section, but the posterior 

 borders are always distinctly separated from the sacs. 



In all the sections of the ganglia a peculiar change occurs after mounting in 

 chloride of calcium, the oily matter of the tissue collecting in curious streaks and 

 circles, and apparently at some parts resisting the penetration of the fluid. 



Considerable difficulty is experienced in making out the anterior branches of 

 the ganglia, from the opacity of the snout ; but three or four trunks of note are 

 occasionally apparent — two large branches superiorly, and one or two smaller 

 beneath. Some twigs seemed to proceed in the direction of the eye- specks, but 

 their ultimate distribution could not be traced. 



The great nerve-trunks (Plate X. fig. 1, n) leave the posterior end of the 

 inferior lobe as in Ommatoplea, proceed along each side of the body, and termi- 

 nate a little within the tip of the tail. Their calibre slightly diminishes as they 

 course backwards ; and their position is nearer the ventral than the dorsal sur- 

 face. Branches no doubt exist, but only faint traces of such are seen in the 

 longitudinal sections, for the opacity of the textures in the living animal prevents 

 their being satisfactorily made out. The trunks are imbedded in a fibro-granular 

 matrix of the same reddish hue, and have, in addition, the proper sheath of the 



