334 APPENDIX. 



large, appearing almost to coalesce, and losing altogether the regular 

 pinnate character. Even in these specimens the caeca can be made 

 easily visible by slight compression between plates of glass. The 

 colour of the central vessel is always alike, and the irregular move- 

 ments of a fluid in it are very perceptible. There is, in most speci- 

 mens, an indentation, more or less deep, on some part of the body 

 — the beginning probably of a separation. 



Clitellio arenarius (page 67). 



"Worm 6 lines long, slender, filiform, slightly narrower at each 

 end, of a reddish colour to the naked eye, smooth, annular, with 

 faint line-like dissepiments, the sides thickened and neatly crenulated. 

 Rings about equal in length to their diameter. Head lanceolate, the 

 mouth inferior. The anal extremity obtuse, deeply sinuate, mutable 

 in form ; for the little prominences which bound the sinus can be 

 opened wide or shut at pleasure. Bristles in four series, equidistant, 

 from two to four bristles in each series ; the bristles ai'e minute, 

 entirely retractile, cui'ved like an italic y, and sharp at the point. 



This worm is not capable of shortening and lengthening the body, 

 but it writhes and wriggles about, rolls itself into more or less com- 

 plete spirals, and progresses like an earthworm by aid of its bristles. 

 When magnified, the body may be described as a sort of transparent 

 whitish tube, containing a red spiral blood-vessel, and a larger dusky 

 intestine, so wreathed and twisted together that they are only seen 

 separate at certain undetermined places. The anterior and posterior 

 portions are paler than the middle, and the rings and bristles there 

 more distinctly visible. The intestine is constricted at regular inter- 

 vals, the portion between the strictures longer than broad, and rough 

 or granulous, and filled with earthy matter. 



This little worm lives in wet gravel or sand on the shore where the 

 water is brackish. It seems to be common. It lives without appa- 

 rent inconvenience in fresh water. That the bristles are in four 

 series is only to be discovered when the body has been compressed. 



The skin of this worm is a clear very faint yellow, so that the red 

 colour of the body depends on its blood-vessels, which run from one 

 extremity to the other ; one large vessel on each side of the intestine, 

 uniting in the anterior segment, and being much slenderer there than 

 they are lower down. The vessels and intestine are straight or tor- 

 tuous, according to the state of the worm as to its contraction or 

 expansion : the latter is usually filled with earthy matter, but is pale 

 or empty at the divisions between the rings. When contracted, the 

 sides are minutely crenulate. The mammiform papillse are obviously 

 connected with the generative function, and are not always present. 

 I have seen them, in a great number of individuals, fully developed 

 in January ; and the ring to which they belong, as well as the one 

 above and below it, are filled with a milk-white matter, over which 

 some fine branchlets of the blood-vessels ramify, and the skin is 

 thickened at the part. 



