238 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



the peristomial disk is approached, the shape gradually 

 changes until it becomes distinctly lenticular. 



Upon the oral face of each tentacle are seated in two 

 irregular rows from two to eight peculiar bodies which 

 have been described as tentacular pedicels (PL XVII., fig. 

 1, t.p.) In shape they resemble a wine glass without the 

 stem (fig. 3, a), and so suggestive of a sucker is their 

 appearance when seen in situ, that the older zoologists 

 may well be excused for comparing them with the tube- 

 feet of Asterids and Echinoids. In minute structure, 

 however, they are entirely different. Each consists of an 

 outer envelope composed of ordinary ectoderm cells (fig. 

 3, b), enclosing a cup-shaped mass of cells, also ectodermal, 

 but of a more specialised kind. They are much longer 

 than ordinary ectoderm cells, especially those which lie 

 at the bottom of the cup, and the nucleus is basal. It is 

 highly probable that the free ends of these cells bear long 

 cilia, but I have not satisfied myself upon this point. 

 Occupying the same position on the tentacles of S. digi- 

 tata are a number of bodies (sixteen to twenty-four), first 

 described by Quatrefages as suckers, and since, by Hamaim 

 as sense organs, which are obviously similar in structure 

 to those just described (PI. XVII. , fig. 2). There are, 

 however, certain important points of difference. The 

 mass of specialised cells does not project above the surface 

 of the tentacle, and the cavity which they surround in 

 S. inhcerens is here occupied by a solid core of elongated 

 cells, the basal ends of which pass into a bundle of nerve 

 fibres which can be traced into continuity with the ten- 

 tacular nerve. Hamann states that the free ends of these 

 cells are ciliated. I have examined my sections of S. 

 inhcerens with a view of discovering a nervous connection 

 if such existed, between the organs I have described and 

 the tentacular nerves, but without success. 



