TRANSACTIONS 



OF THE 



statural Jistorg Swrijetg of (Slaspfo- 



Ichthyonema grayi* (Gemmill and V. Linstow). 



By James F. Gemmill, M.A., M.D, 



[Read 24th September, 1901.] 



Large nematode worms from specimens of the common sea- 

 urchin taken from different localities in the Firth of Clyde. 



The worms were unattached, and lay coiled up within the 

 perivisceral cavity of their hosts, exhibiting during life con- 

 tinual gentle sinuous movements. 



Females. 



The females, when mature, measure from 600 to 1,500 mm. in 

 length, and from 2 to 4 mm. in breadth. Not more than four 

 occurred in any one sea-urchin, and in one case only a single 

 large specimen was present, which measured quite five feet in 

 length. (This specimen I succeeded in preserving and mounting 

 entire.) 



The body is covered by a delicate cuticle, and tapers at both 

 extremities, each of which carries a very small hook-like cuticular 

 process. The tail is slightly blunter than the head, and is 

 usually curved ventrally in a half circle. The body is semi- 

 transparent, with an opaque white strand — the ovary — running 

 along the ventral wall. The body is sharply constricted for 

 about half-an-inch near its middle part. Running along the 



*A fuller account of this species is given in Archiv fur Naturgeschichte, 1902. 



