126 Prof. P. M. Duncan on the 



laiit, to the base of the cup below the calcareous structure. 

 They are often slightly wavy, nucleated, and unstriated (see 

 also Haraann, op. cit. pi. xiv. fig. 7). 



The circular fibres are placed over a delicate mem- 

 branous tissue which may sometimes be seen projecting 

 beyond the cut end of a tentacle, and this is clearly epithe- 

 liate and very minutely granular. Probably it is ciliated, 

 but no trace of cilia came nnder observation. The longi- 

 tudinal fibres are usually somewhat coloured naturally at the 

 peri])odia, and arise by broadish bases, and soon attenuate ; 

 they are apparently separate and not in fascicles. As is the 

 case around the origin of the muscles of the spines, there is a 

 very fine lax entanglement of threads much less in diameter 

 than the thinnest muscular fibre around the peripodium, and 

 it is apparently nervous in character. The nerves have 

 small simple ganglionic swellings, and conform to Loven's 

 well-known description, except that I have not seen multi- 

 polar cells uniting. 



The tentacles which are between the ambitus and apical 

 system are larger than those situated actinaliy, and their 

 calibre and middle space are greater, the muscular walls are 

 more attenuate, and the cup end is more tumid and smaller. 

 These tentacles have a more baggy appearance than the others, 

 and when decalcified the muscular layers are very distinct, 

 especially the transverse or circular series, which is so feebly 

 developed m the actinal set. In fact these tentacles resemble 

 in a minor degree the similarly placed structures of 

 Sahnacis. 



The muscular fibres which close in the free end of the 

 tentacle pass inwards from the stout continuous calcareous 

 spicules which form the foundation of the circlet of calcareous 

 reticulation of the cup ; this more or less quadrangular con- 

 tinuous structure Lov6i has called the foot-ring or " psellion'^ 

 (Loven, op, cit. pp. 49, 50). The muscular fibres unite at 

 the centre of the neck of the tentacle and form the floor of 

 the sucker or adhering apparatus. 



The psellion is so arranged that the spoke-like spicules of 

 the four parts of the calcareous circlet spring generally from 

 the middle of one of the four main spicules of it, and the 

 junction of one main spicule with another marks the line of 

 separation of the parts of the circlet (figs. 26, 27). Imme- 

 diately below the psellion are two very slender spicules of the 

 same length, and they are connected by vertical and distant 

 short spicules. Sometimes a ragged areolar lamina extends 

 slightly over the edge of the muscular circle. 



The calcareous circlet of the cup, springing as it were from 



