322 ORGANS OF DIGESTION. 



sea. The ramifications of the long, thick, and longitudinally 

 striated tentacula of the actinia arbor ea (Fig. 112. B.) render 

 that isolated polypus, which is more than a foot in height, 

 still more dendritic in outward form than the last species ; 

 and the smaller size of its body (B. a. b.) makes it more nearly 

 approach to the higher stellated echinoderma, as the ophiura, 

 comatula, and euryale, where the nutritive organs are con- 

 fined, as here, to a small central disk. The deep blue-colour- 

 ed disk around the mouth (112. D.), between the thick bases 

 of the ramified tentacula, is here also marked with numerous 

 brown-coloured spots, regularly disposed on yellow bands 

 radiating from the mouth to the margin of that surface, and 

 the dichotomous character of the branched tentacula (112. B. 

 b. c.) is seen even in the minute fleshy tubular filaments (B. 

 d. d.) which cover the terminal tubercles of all the branches. 

 The adhesive mucous exudation from the surface of all those 

 ramified tentacula, as in other actinia, inflames and irritates 

 the human skin, and may serve alike to seize and to destroy 

 the victims which fall within their grasp. In the pedun- 

 culated form of the lucernaria, with its soft irritable body 

 and central digestive simple sac like an actinia, and its 

 connected radiating pedigerous divisions, we are also ap- 

 proximated to the condition of the higher stellated echino- 

 derma, and especially to the pedunculated crinoid family, so 

 that, from the simple isolated sac of the hydra, which is 

 alike generative and digestive in every part, we pass through 

 a great and most diversified series of zoophytic forms, to the 

 complicated structure of these large independent actiniform 

 polypi, where separate parts of the body are already dis- 

 tinctly appropriated to the most general and important 

 functions of organic life. 



IV. Acalepha. The soft transparent gelatinous acalepha, float- 

 ing like large animalcules through the sea, are but free digestive 

 cavities, like inverted zoophytes detached from their stony 

 axis, and have their alimentary organs extended through every 

 part of their mantle, their long filiform tentacula, and their 

 pendent ramified peduncles. Among the ciliograde acalepha, 

 the beroe'pileus has a straight alimentary canal passing through 

 the long axis of its body, commencing at the lower part with four 

 thin prominent contractile and highly irritable lips surround- 

 ing the wide oral aperture. The contracted oesophageal part is 



