igoS.] J. Stephenson : The Anatomy of some Aquatic Oligochceta. 273 



coating on the surface of the body, in which the foreign particles are entangled; this 

 is presumably a mucoid secretion produced by the epidermal cells. 



The prostomium is rounded, and not at all pointed or conical; in some animals, 

 perhaps recently separated, it is even flattened in front; it is provided with sensory 

 hairs. There is a pair of eyes, at the level of the mouth, laterally situated, the 

 black pigment of which they are composed having, as in A^ais variabilis, a violet 

 tinge. One eye may be smaller than the other ; there are sometimes numerous 

 '' Nebenaugen" in the vicinity (plate xviii, fig. 35). The skin of the general surface 

 very often contains numLcrous small masses of pigment, of a more or less circular, 

 or it may be quite irregular form ; their relative size may be seen in plate xx, fig. 50, 

 and will be observed to vary from mere points upwards. In animals which possess 

 this pigmentation the pigment is of a brown colour, and is almost absent from the 

 first five segments ; it is absent again from several segments at the posterior end of 

 the animal, and, as seen in the figure, from the newly-formed segments at the zone 

 of budding. The extreme posterior end of the animal, immediately around the 

 anus, is ciliated, the cilia being an extension of those which here, as elsewhere, 

 line the intestine. 



The skin bears a number of small sensory papillae ; these are projections of 

 the shape of a truncated cone, or are sometimes cylindrical; they bear a number 

 of minute stiff hairs on their summit ; they are clear, colourless, and not covered 

 by foreign particles. 



Their distribution is somewhat variable ; they may, for example, be arranged 

 fairly regularly in rows across the dorsal surface of the animal, one row in 

 each segment from the anterior to the posterior end ; or they may be absent 

 from the posterior end of the body ; or they may be segmentally arranged as far back 

 as the sixth segment, and be less numerous and less regular behind this; or 

 the converse may be the case, i.e., the segmental arrangement may be better 

 marked behind the sixth segment than in front. The prostomium may or may not 

 bear them ; the ventral surface appears to be altogether without them ; and they 

 frequently seem to be especially well-developed in two lines along the lateral surfaces 

 of the body. 



The level of the transverse rows of papillae is that of the insertion of the dorsal 

 setse in each segment. The papillae are not themselves retractile, but the papilla 

 as a whole may be (probably temporarily) depressed into a slight pit on the external 

 surface of the body, from the bottom of which it then appears to arise. 



The number of segments varies considerably. The spiallest number counted 

 was 23 ; several animals were noted as having over 40, in one case 46. There is a small 

 region of the bod}^ posteriorly where definite segments are unrecognizable, not 

 as yet having been differentiated The first five segments may be very short. 



A number of specimens were seen which I was at first inclined to regard as 

 pathological. They possessed no distinctly differentiated head (plate xx, fig. 51), no 

 eyes, and no recognizable pharynx. That the portion of the animal shown in the figure 

 is the anterior end is evidenced by the long setae ; and what has presumably happened 



