243 
cola marina, showing a giant cell and its process in which 
the neurofibrille are seen; also sheath of neurilemma 
enclosing the cord; fibrous part of cord partially sub- 
divided by a median sheet of neurogla; 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 
ot which are seen; two oblique muscles and the coelomic 
epithelium. x 500. 
Fig. 55. Horizontal section of fourth chetigerous 
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 cheetigerous annulus. x 165. 
Vig. 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 
notopodial sete, the gills, and the otocyst. x 950. 
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 he the otocysts (outline 
dotted), the achztous body segment and the first cheeti- 
gerous segment. The peristomium and the achetous 
segment are divided into two, thus forming four annul, 
corresponding to the subdivision of this region in adults. 
Cig. 0. x 200: 
Fig. 58. Ventral view of the corresponding portion 
of a post-larval specimen 35mm. long. The mouth is 
situated on the anterior edge of the peristomium and the 
two cesophageal connectives are seen uniting in the third 
annulus. Cf. fig. 6. -x 100. 
Fig. 59. The prostomium and nuchal organ drawn 
