562, T, A. STEPHENSON 
mesenteries appear in exocoels, and usually the musculature 
of the body-wall ectoderm is lost. The habitat of the forms 
with vesicles and elaborate tentacles is often tropical. ‘Text- 
fig. 18 gives a good example of one of the forms with a frill 
of vesicles. The crown of tentacles (unshaded) is seen to be 
surrounded by a wider corona of compound vesicles, like a ruff, 
Trxt-Fic. 19. 
Actinodendron plumosum, copied from a photograph of 
a living specimen by W. Saville-Kent. See acknowledgement 
on p. 496. An example of complexity affecting tentacles and disc. 
projecting beyond it. A vertical section of the same form is 
shown in Text-fig. 2, a. A ease in which the tentacles are 
dendritic and form a frill, being borne on permanent arm-like 
projections of the disc, is shown in Text-fig. 19, and other 
variations in Text-figs. 14 (tentacles) and 1 (acrorhagi). 
In Mesomyaria, on the other hand, we get the sphincter, 
