238 
it are covered with chlorogogen celis. (See fig. 45.) The 
nerve cord is divisible into a dorsal fibrous mass, in the 
mid-dorsal line of which one giant-fibre is seen, and a 
ventral portion composed largely of nerve cells the nuclei 
of which are indicated. x 58. 
Fig. 56. Transverse section of the same specimen in 
the region of the last nephridium. ‘To the right of the 
two vertical lines was drawn from a_ section passing 
through the anterior part of the ninth chetigerous seg- 
ment, while the portion on the left is from a section passing 
through the tenth parapodium, and showing the notopo- 
dium with its setal sac and protractor muscles and the 
whole length of the neuropodium. We see also a portion 
of a gill, with its afferent and efferent vessels, the funnel 
(opening into the ecelom) and excretory part of the nephri- 
dium, the stomach with its ventral groove and blood 
sinuses, the subintestinal and the lateral gastric, the dorsal 
and ventral vessels, the latter surrounded by chlorogogen 
cells (fig. 45), the muscles of the body wall and their blood- 
vessels; two oblique muscles; the nerve cord, the dorsal 
fibrous mass of which contains two giant-fibres, and the 
ventral portion with nerve cells, the nuclei of which are 
shown. x 38. 
PLatTeE V, 
Fig. 37. Longitudinal section of the heart of a young 
Arenicola 65 mm. long to show the heart body in an early 
stage of its formation. On the posterior (right) side and 
also on the antero-exiernal side (left of the figure), the 
wall of the ‘heart is being invaginated at several points, 
thus giving rise to the heart body. x 100. 
ig. 38. A portion of the wall of the ventricle from 
the point marked + in the preceding figure, and composed 
