(^tlie Sertularia Gelatinosa of' Pallas. 85 
denticles, in a single one, or in a clavate mass, containing the 
rudiments of a future denticle and polype. 
The denticles are terminal, and are supported on short foot- 
stalks which issue from the stem in an alternate order. They 
are bell-shaped, somewhat produced, with an entire margin. 
The vesicles are ovate, approaching to cylindrical, with a con- 
tracted truncated mouth, covered with a hemispherical lid. They 
are solitary, nearly sessile, and arise in the divisions of the bran- 
ches or of the foot-stalks of the denticles. At the point of separa- 
tion of the larger branches there is usually a small twig, sup- 
porting two or three denticles with vesicles. 
The stems are of a brownish colour, opake, and of a firm 
tough consistence, but in approaching the extremities they be- 
come soft, colourless and transparent, so that the central stem of 
the polype can be easily distinguished. Immediately above 
every division, whether formed by a branch or foot-stalk, there 
are several transverse wrinkles, varying in number, being sel- 
dom fewer than three, or more than six. Similar wrinkles oc- 
cur on the foot-stalks at the base of the denticles. The stems, 
at the divisions of the branches, are a little thickened, while 
the foot-stalks at the base of the denticles are slightly attenuat- 
ed. 
The body of the polype is distinctly visible through the 
transparent covering. In the branches it is somewhat dusky, 
but becomes paler towards the denticles. The foot-stalk of the 
polype, which corresponds with the foot-stalk of the denticle, 
is narrow, but it suddenly enlarges in the denticle to form the 
body, nearly of the same shape with its covering, at the sum- 
mit of which the tentacula are disposed in a circle. These are 
about twenty in number, linear, blunt at the extremity, and di- 
vided into about ten rough raised joints. Above the circle of 
tentacula there is a globular head, containing the mouth. The 
polypes are not very irritable ; for, even when pricked with a 
needle, they seldom retreat completely within their covering, 
and when left at rest, soon expand themselves, the summit of 
the body becoming even with the margin of the denticle, and 
the tentacula diverging or folding backwards on its external sur- 
face. When in an active state, I have observed the water 
taken in at the mouth descend, for the space of several seconds, 
through the gelatinous parenchyma of the body and foot-stalk. 
