ALC YONIUM. 125 
Again, the organs, such as muscles, gonads, and gastric 
filaments, are much more definite. Thirdly, the ccelen- 
teron is not simple but partially divided thus :— 
A, Gastric cavity for digestion. 
B, Radial cavities — nutritive and 
vascular, walls form motor 
(muscles), skeletal (mesen- 
teries), and reproductive 
(gonads) organs. 
Lastly, the ectoderm is tucked in to form a gullet. At 
the same time we may note the absence, as in Hydra, of 
definite respiratory, excretory and blood-vascular organs. 
C@:LENTERON<® 
IV.—ALCYONIUM. 
PHYLUM CQELENTERATA. 
CLass ScYPHOZOA. 
SuB-CLAss ACTINOZOA, 
ORDER OCTACTINIA. 
Fig. 57-—ALcYONIuM DiciTatum. (Ad nat.) 
A B Gonad. Coenosarcal 
Canal. 
Longitudinal 
Muscle. 
Directive 
Mesentery. 
Body-wall of Polype. 
A, Isolated spicules. B, A tangential section through the entire colony showing 
the polypes in cross section. 
Alcyonium digitatum (Dead Man’s Fingers) may be taken asa 
type of the colonial Actznozoa. The colony may be fixed at its base to 
a foreign body and branching like a coral, or it may grow closely 
adherent to the tube of an annelid or other body. It is found most 
