378 IV. C. APINTOSH [may 



structure, but the authors incline to subdivide it into two, from slight 

 differences in the bristles; the second from the 15th to the 25th 

 segment. Each segment bears capillary bristles dorsally, and spoon- 

 shaped ones inferiorly. The latter they compare with a similar type 

 in Polydora and JEphesia. These bristles in the middle or abdominal 

 region are of service to the animal in its movements in the tube, and 

 consequently undergo certain changes from friction. 



The authors found a second and large form (C) somewhat resembling 

 the foregoing in April, but rarely, viz. in the proportion of 1 to 100 

 of the first-mentioned. It measured about an inch and a half. The 

 segments in the middle region are long, while those anteriorly and 

 posteriorly are very short. It is of a pale colour, with two orange- 

 red eyes. The palps are fully developed. Capillary bristles occur in 

 the first 6 segments. From the 7th to the 26th the dorsal fascicle is 

 composed of long pelagic bristles ; from the 27th to the 30th of pelagic 

 bristles and spoon-shaped forms ; while in the terminal segments it 

 agrees with the previous form. Ventrally the spoon-shaped bristles 

 also correspond with the latter. 



In this form a change, chiefly in the pelagic condition of the 

 bristles, 1 the elongation, and less pigmented condition of the median 

 segments, has occurred. The animal is comparatively sluggish, and 

 secretes abundant mucus, in which the eggs may be placed, though 

 none were seen in it. The genital products fill the body-cavity, the 

 ova (for all were females) being yellowish-brown. The segmental 

 organs open between the feet as in form A — at a higher level than 

 those of B. The wall of the digestive tube is atrophied, but to a less 

 extent than in the latter, and the animal takes food. 



The third form (B) is the epitokous pelagic one, which differs very 

 considerably from the foregoing, and also from the first form. It was 

 originally noticed by Verrill in the Bay of Fundy, and specific distinction 

 given it — as Hcterocirrus fimbriatus. This second variety, also rare, is 

 recognised by its great activity, for on escaping from the Lithothamnion 

 it swims rapidly through the water like Nephthys. It has a more 

 slender form. The central region is enlarged by the genital products, 

 and cylindrical. The posterior region is comparatively small, with a 

 slightly spatulate extremity. The muscles of the body- wall are feeble. 

 The anterior and posterior regions are greenish-brown, the middle bright 

 yellow. The eggs are brownish. The head differs from the typical 

 form (first-mentioned) by the presence of two large eyes, in addition to 

 the ciliated furrows. The anterior region agrees in regard to bristles 

 with the first form, except that they are somewhat longer. The palps, 

 however, are reduced by absorption to mere buds, and the branchiae 

 are short. In the anterior part of the abdomen the spatulate bristles 

 have disappeared, and the greater part of the abdominal region is 



1 The elongation of the setae of the antennae of the ostracod, Philomcdes, at the period 

 of general maturity, is a parallel instance. 



