480 G. HERBERT FOWLER. 



lar chamber (H. N. M.) formed by the oral disc, from which radiate the 

 tentacular pouches. A few tentacles are cut at various angles. At the 

 bottom of the tentacular chamber is the opening into the stomodgeum, and 

 through it into the ccelenteron. A few central plates of mesenteries project 

 from the upper surface of the inturned column. 



Figs. 14 — 18 are taken from a series transverse to the animal, and repre- 

 sent longitudinal sections of the same retractor muscle, &c.,at various heights. 

 Compare p. 468 and Pig. 23. 



Figs. 19 — 22 are taken from a series vertical to the plane of the pedal 

 disc, and are therefore transverse to the retractor muscle. They exhibit the 

 way in which it appears to be shifting in position away from the mesentery. 



Fig. 23. — Diagrammatic vertical section of the animal, slightly less con- 

 tracted than Fig. 10; it shows both sides of a large mesentery with retractor 

 muscles. The position of the circular " mesodermal " muscle-fibres, which 

 in combination with the retractors achieve the inturning of the upper part of 

 the column, is indicated by dots. 



