268 J. T. CUNNINGHAM. 



which commence as processes of certain colossal ganglion cells 

 occurring in definite positions in the brain or ventral cord. 

 He gives the following account of the giant-fibres in the genus 

 Sthenelais. There are three kinds of colossal nerve-fibres : 

 (1) some traversing the whole nervous system from the 

 anterior to the posterior extremity ; (2) some running from the 

 posterior to the anterior extremity; (3) some starting from 

 the nervous system on each side, and running to the periphery. 

 He further says that if the nervous system be traced through a 

 series of transverse sections he finds in the posterior part of 

 the brain a colossal ganglion cell on each side which sends off 

 a large process. This process passes first forward for some 

 distance into the brain, then through the oesophageal commis- 

 sure into the ventral cord. These two nerve-fibres unite into 

 one which runs ventrally on one side of the ventral cord to the 

 posterior extremity of the body. This colossal nerve-fibre is 

 enveloped by a fibrous sheath, which is at first closely applied 

 to it, but in its further course separates from it, and then 

 encloses a cavity which becomes larger posteriorly, and in the 

 middle of the body attains an enormous diameter. 



Unfortunately, no figures illustrating these descriptions have 

 yet appeared, and I have therefore had to confine myself to a 

 comparison of my own sections with the above description. I 

 have been totally unable to see the connections which Rohde 

 declares to exist. I have prepared series of sections from 

 different parts of the body ofSigalion boa, Johnston, which, 

 according to Mcintosh (Invert. Fauna of St. Andrews), belongs 

 to Kinberg's genus Sthenelais. In the middle region a pair 

 of colossal fibres, or as I shall usually call them, neural canals, 

 appearing under a low power like tubes, are conspicuous. 

 One of these is situated on the inner side of each cord, 

 towards the dorsal region, and at the periphery of the cord 

 (fig. 22). The neural canal is internal to the layer of ganglion 

 cells, and is partially occupied by a shrunken homogeneous 

 substance. Processes can be often seen passing off from the 

 ganglion cells transversely, and entering the substance of the 

 cord where they are seen to branch into fine fibrils, exactly in 



