SEA-FISHERIES LABORATORY. 323 



cola marina, showing a giant cell and its process in which 

 the neiiroflbrillae are seen ; also sheath of neurilemma 

 enclosing the cord ; fibrous part of cord partially sub- 

 divided by a median sheet of neuroglia ; two giant fibres ; 

 nuclei of small nerve cells situated in ventral part of cord ; 

 root of a spinal nerve on the right ; epidermis ; circular 

 muscles ; longitudinal muscle bands, the fibrils and nuclei 

 of which are seen ; two oblique muscles and the ccelomic 

 epithelium. x 300. 



Fig. 55. Horizontal section of fourth chsetigerous 

 segment of a specimen 45 mm. long passing through the 

 ventral nerve cord, to show the giant-cell and the spinal 

 nerves. A pair of nerves is given off from the cord oppo- 

 site each inter-annular groove and in addition a nerve or a 

 small bundle of nerves to the chsetigerous annulus. x 15. 



Fig. 56. A post-larval specimen 3'9 mm. long taken 

 in the tow-net near Lytham. The animal is seen from the 

 left side, and shows the eyes on the prostomium, the seg- 

 mentation and annulation, the parapodia, the two kinds of 

 ootopodial setse, the gills, and the otocyst. x 50. 



Fig. 57. Dorsal view of anterior end of a post-larval 

 specimen 5'4 long, to show the prostomium, the nuchal 

 organ, the peristomium in which lie the otocysts (outline 

 dotted), the achsetous body segment and the first chseti- 

 gerous segment. The peristomium and the achsetous 

 segment are divided into two, thus forming four annuli, 

 corresponding to the subdivision of this region in adults. 

 Cf. fig. 5. x 100. 



Fig. 58. Ventral view of the corresponding portion 

 of a post-larval specimen 3*5 mm. long. The mouth is 

 situated on the anterior edge of the peristomium and the 

 two oesophageal connectives are seen uniting in the third 

 annulus. Cf. fig. 6. x 100. 



Fig. 59 The prostomium and nuchal organ drawn 



