22 DEVELOPMENT OF 



residence in Iceland in tlie spring of 1840, on some in- 

 dividuals in that stage of development which was origin- 

 ally named 8cyplmtoma by Sars, and which were appa- 

 rently of the same species as those observed by him, or 

 at least corresponded entirely with his description of their 

 external form (in his work of 1835.) The few specimens 

 referred to were taken outside the so-called battery near 

 Keikevig, and under rather unusual circumstances, for 

 they occurred at an inconsiderable depth affixed on the 

 internal surface of some Modiolus shells and not on algae. 

 This circumstance afforded me the advantage during the 

 time I kept them in fresh sea water, of being unimpeded 

 by the mucus with which the vessel in which they are 

 placed is immediately filled, when it contains some of the 

 plant also, and of being able to detach thin laminae of 

 the half-disintegrated shell with the animals adherent, 

 for the purpose of microscopic observation, without 

 disturbing or injuring them in the slightest degree. The 

 number of tentacula was 28 — 30. The usual form of 

 the body varied from that of an inverted cone, to a cup 

 or bell shape (fig. 35.) The mouth of the bell was sur- 

 rounded by an extraordinarily moveable lip or annular 

 membrane which passed round within the circlet of ten- 

 tacles, and allowed of such expansion that the mouth of 

 the bell could be rendered equal in size to the diameter 

 of the body ; it was also capable of contracting so as to 

 close the bell completely and of being extended, so as to 

 equal the length of the tentacles, in which condition it 

 was always quadrangular. When the annular membrane 

 was extended in this way (fig. 40,) it could be readily per- 

 ceived that a vessel or rounded canal ran down each of 

 the four angles; that these four vessels were connected at 

 the border of the opening with a circular vessel; and that 

 they were also united at the base by another and 

 larger circular canal, which ran along the circle of 

 tentacula. Into this larger circular canal, and opposite 

 to the four longitudinal canals of the annular mem- 

 brane, the four ridges which were observed on the 



