562 P. W. GAMBLE AND J. H. ASH WORTH. 



cesses (C. P.). The notopodial setse are in two rows, those in the anterior 

 row being about two thirds the length of those in the posterior row. X 2. 



Fig. 32. — View of the same region from the left side. Note the cirriform 

 process just dorsal to the last neuropodium {Ni/i.). The other features are as 

 in the previous figure, x 2. 



Fig. 33. — The tenth brauchiferous annulus of a specimen of A. cristata, 

 120 mm. long, from Captiva Key, seen from the left side, to show the small 

 greyish pit situated on a slight elevation just dorsal to the neuropodium. 

 There is a similar structure on each of the last seven chsetigerous annuli of 

 this specimen. The anterior row of shorter setae and the posterior row of 

 larger setae are shown (slightly displaced) in the notopodium. 



Fig. 34. — Post-larval specimen of A. marina, 3'9 mm. long, taken in the 

 tow-net by Mr. R. L. Ascroft at Lythani. The animal is seen from its left 

 side, and shows the eyes on the prostomium, the two kinds of notopodial setae 

 (see also Pi. 23, fig. 12), the gills, and the otocysts. From a preparation. 

 X 50. 



Fig. 35. — Post-larval specimen of Arenicola ecaudata, 9"4 mm. long, 

 Port Erin, August, 1896. The figure is from the left side of the animal, 

 and shows the external characters and nephridiopores. There is a distinct 

 groove separating the peristomiuni {Per.) from the following achsetous segment. 

 The first chsetigerous segment is therefore (as is further explained in the text, 

 p. 441) the third segment of the body. X 22. 



Fig. 36. — Another post-larva of A. ecaudata (8 mm. long), lightly stained 

 and then cleared in cedar-wood oil. The anterior half is viewed obliquely from 

 the left side and ventral surface, tiie posterior half is twisted upwards and 

 seen from the ventral surface. The alimentary canal is shaded, the nerve -cord 

 left white. The nephridia of the right side are clearly shown. Note aUso the 

 otocyst (Ol.) with its single otolith. X 24. 



Fig. 37. — Posterior extremity of the same specimen, to show the presence 

 of crotchets in the last six notopodia in addition to the capillary setae. The 

 intestine {Int.) is drawn out into concertina-like folds by the sepia {Sp.). X 130. 



PLATE 25. 



Fig. 38. — Longitudinal section of the heart of a specimen of A. Grubii 

 140 mm. long from Port St. Mary. The wall of the heart is thin, and 's com- 

 posed of three layers, — an endothelium internally, a muscle layer, and a peri- 

 toneal covering, the cells of which often contain chlorogogenous granulf;s. The 

 muscle layer is only feebly developed in worms of this size, it becomey much 

 more highly developed in older specimens (see Fig. 39). On the pcj>stcrior 

 (right) side the wall of the heart is being invaginated at several points, thus 

 giving rise to the heart-body. Each invagination involves the whole wall of 



