54 DEVELOPMENT OF 



turned round on its axis, it is then easily seen that the 

 collar is constituted by a fold or border of integument, 

 and that it descends rather lower on the abdominal than 

 on the dorsal aspect, and also that it is deeply incised in 

 the middle of its abdominal portion. The sharp border 

 of the collar is more or less regularly serrated, and the 

 small teeth formed by these serratures have given rise to 

 the name echmata applied to this species, under the sup- 

 position that it is the same with that of Siebold, and that 

 the above described organ may be designated as " a cir- 

 clet constituted of blunt spines around the mouth." 

 Under sufficient illumination, and when the part is 

 slightly compressed between slips of glass, there may be 

 distinguished in the substance of the collar and within 

 the integument numerous spiculse or spines, which form 

 as it were in the collar a circle around the oral orifice. 

 These spines are placed with their thicker ends towards 

 the mouth, alternately near it and further off, in two 

 concentric ckcles, and the opposite and smaller extremity 

 of each spine passes into one of the teeth of the collar. 

 The position of the oral orifice, in consequence of the 

 various contractions of the body, seldom coincides with 

 the most anterior part of the animal, but is usually placed 

 somewhat below it on the abdominal surface ; the margin 

 of the mouth can be so much protruded, as to appear like 

 a suctorial acetabulum surrounding the orifice. There is 

 also a sort of pharynx, but it does not appear to be mus- 

 cular. A little behind the middle of the body, is seen a 

 rather larger sucker (the abdominal) wliicli is somewhat 

 depressed in the centre, and the margin of which can be 

 expanded in various ways. Close to the root of the tail 

 is a transparent spot, surrounded by an abrupt dark 

 coloured border, and appearing like an interior cavity 

 with contractile walls, it is in fact however, only the root 

 of the tail which is seen through the body. On the other 

 hand, close before this there is a much smaller circular 

 spot, which is an opening or pore. Of the internal organs 

 which are visible through the semitransparent integument, 



