462 
EDITH M. JIUSGEAVE. 
within the “ gastric cavity.” ^ Of this interesting Pennatulid 
he writes : “The anterior part of the body being well dis- 
tended, an active peristaltic contraction of the circular 
muscles takes place, and the fluid is thus forced backwards 
into the posterior region (peduncle). The latter consequently 
becomes elongated, somewhat as the ambulacral ‘ foot ’ of an 
echinoderm is protruded, and the body is pushed forward a 
short distance. The circular muscles then relax and the longi- 
tudinal ones contract in such a manner as to pull the posterior 
region forward towards the anterior part which adheres to 
the bottom. By the constant repetition of this process the 
whole organism moves slowly forwards. The ci*eeping’ move- 
ments are very irregular since the action of the muscles is 
not uniform.” 
In large and robust Pennatulids having a central, more or 
less rigid, calcareous axis, certain modifications of structure 
have arisen which apparently play an important part in 
inducing and maintaining a comprehensive circulation of 
fluids throughout the colony. 
In all the genera examined the musculature of the body- 
wall becomes attenuated towards the base of the stalk (figs. 
12, 13, 14), its place being occupied by the spongy distensible 
tissue which is so abundantly provided with apertures into 
the large canals, and also with a definite number of apertures 
(which appears to be constant on each species) to the exterior 
(figs. 1, 2, 3, 4). In living specimens this region is often 
considerably dilated by the absorption of fluids by the canals 
of the spongy tissue, so that the stalk terminates basally in a 
small distended bulb, which, if buried in the mud of the sea 
bottom, may materially assist in supporting the colony in a 
vertical position. 
The distension may also represent the initial stage of the 
peristaltic movements of the stalk and rachis commented upon 
elsewhere (p. 473). 
* By the teim “ gastric cavity ” Wilson, no doubt, means the spaces 
occupied by the large central canals of the stalk and rachis. 
