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XII.— On some Points in the Structure 0/ Tubifex. By W. C. M'Intosh, M.D., 



F.R.S.E. (Plates IX., X.) 



(Eead 2nd May 1870.) 



At least two species of Tubifex are abundant in Scotland, one of which is, 

 perhaps, more prevalent in streams, the other in lakes. The former is common 

 at the margin of the river Tay, when the water is low, in sandy tubes of little 

 tenacity, and often in tunnels formed amongst the wet sand under stones, just 

 as many of the marine annelids occur. Its length varies from three-fourths of 

 an inch to an inch and a-half when stretched, and the segments range from fifty 

 to seventy, the average number probably being sixty. The body is of various 

 shades of dull fawn or pale madder-brown, somewhat interrupted by the pale 

 bands at the junctions of the segments, and streaked by the reddish dorsal 

 vessel ; or, in summer, marked anteriorly by the whitish mass of the reproductive 

 organs. It is easily recognised amongst its fellows by its faintly purplish or 

 lilac hue, as well as by its peculiar mode of progression ; and not a few are 

 observed with reproducing heads and tails. This form, perhaps, has most claim 

 to be called Tubifex rivulorum. 



The body is tapered towards head and tail, distinctly segmented, and much 

 shorter and stouter than the succeeding species. Moreover, the length of the 

 bristles does not equal the diameter of the body. The snout is somewhat- 

 conical, with the puckered mouth at its posterior margin, near the first crenation, 

 which indicates its separation from the succeeding segment. There are many 

 motionless microscopic processes on the surface of the snout in well-developed 

 specimens, and the same organs occur on the bristle-papillse and the caudal 

 segment. Such have generally been regarded as tactile papillae. Though 

 analogous, they are not quite homologous with similar processes in the Turbel- 

 laria. The second segment bears a long bristle at each side dorsally, and three 

 hooks, one of which is small. The third segment has two bristles and three 

 hooks on each side superiorly ; ventrally four hooks on each side. Generally 

 the inferior hooks are five or six in number on each side, one being short and 

 in process of development. The bristles (Plate IX. fig. 1) seem slightly stouter 

 than those of the longer form, and no serrations are visible on the sides. M. 

 d'Udekem noticed in his form a bristle with a brush-like tip, and has figured 

 the same,* but though Mr Lankester has seen such in examples of Tubifex 



Hist. Nat. du Tubifex, &c. ; Mem. couronnes et Mem. des sav. etrangers, &c. ; l'Acad. Roy. de 

 Belgique, torn. xxvi. p. 11, Plate II. fig. 8. 



v qL. XXVI. PART II. 3 U 



