

CALIGOIDEA. I333 



while the animal is swimming, and when attached to the body of the 

 fish, are commonly extended by the side of the abdomen. 



The Nervous System.— The nervous system in Caligas contains but 

 two ganglions, and these by their close approximation appear to com- 

 pose but one. They are situated directly behind the eyes, one above 

 the oesophagus, and the other below it, and are so intimately con- 

 nected on each side of this portion of the alimentary canal, that it is 

 impossible to separate them (fig. 1 s). Indeed, it would scarcely con- 

 vey an incorrect idea of the form, to describe it as a single mass, with a 

 longitudinal cavity through the centre, for the passage of the oeso- 

 phagus. The size of the united ganglions is rather greater than that 

 of the buccal mass. The nerves arising from these ganglions are flat, 

 fibrous cords, enclosed within a membranous envelope or neurolemma. 

 This neurolemma is often one-fourth wider than the bundle of nervous 

 fibres contained within, and these fibres appear to pass through with- 

 out any attachment. The neurolemma is sometimes slightly folded, 

 which gives a crenated appearance to the margin of the nerve. 



The proper cephalic ganglion has a broad ovate or subcordate form. 

 It gives off three pairs of nerves. 



The first pair (a, fig. a) leave the central part of the anterior 

 margin and pass directly to the eyes. As the eyes are adjacent to 

 the ganglion, these nerves are very short. 



The second pair (b, fig. s) arise from the same margin laterally, 

 and extend upward towards the cups (fig. q), passing just within the 

 articulating process of the cephalic segments. Each gives out large 

 branches, which are distributed to the surrounding muscles and tegu- 

 ments. The anterior extremity which goes to the cup is scarcely one- 

 third the size of the base. 



A small tubular vessel (fig. 1 q) extends from the middle of the front 

 along the median line, and appears to terminate in a bulb, about half 

 way to the ganglion. This vessel has been the subject of much inves- 

 tigation, without removing all the doubts respecting its nature. When 

 separated from the body, it appears to be a large neurolemma, con- 

 taining two small bundles of nervous fibres, and this is our final con- 

 clusion, though adopted with some hesitation. It appears probable, 

 from the result of some of our dissections, that this bulb receives a 

 nerve from each side, which either arises directly from the cephalic 

 ganglion, or is a branch of the nerve last described. 



334 



