242 Natural History of British Zoophytes. 



of any spontaneous efforts of the animal, or are accompanied with 

 any kind of perception or consciousness in these animals, which have 

 never been found to present a single nerve in their bodies. The in- 

 dependent nature of the motion of those minute respiratory organs 

 is observed when we cut off the tentacula altogether ; and observe, 

 that they still continue the rapid vibration of their cilia; and though 

 severed from the polypus, the tentacula continue to move forward 

 through the water ; the severed tentaculum of a flustra is seen to 

 swim through the water like a worm. The number of those organs 

 varies much ; they are eight in Serialaria lendigera, and in Plu- 

 mularia falcata, fourteen in Cellaria avicularia, twenty-two in Flus- 

 tra carbasea. The effect of those motions of the cilia again is ob- 

 viously to change the stratum of water constantly in contact with 

 the most delicate fleshy parts of those zoophytes, with the highly 

 organized soft irritable fleshy polypi. Thus they aerate the cellular 

 texture of their body, at the same time that they bring the animal- 

 cules — their ordinary food — within the grasp of the tentacula."* 



All polypes — ascidian and hydraform — subsist on animal matter, 

 and probably only feed upon it in a living state. The smaller spe- 

 cies seize on worms and animalcules brought accidentally within 

 reach, or carried into the vortex formed by the play of the tentacu- 

 lar cilia : the larger kinds (Helianthoida) swallow small crabs and 

 shelled mollusca, rejecting the shells after having sucked out the 

 soft contents. The food, in the Hydroida, is dissolved and neces- 

 sarily made chylous in the stomach, and directly absorbed from it ; 

 but in the ascidian it is probable that the process of chylification 

 is not completed until the food has passed into the intestine. In the 

 higher animals the chyle is mixed with the blood and exposed to 

 the influence of atmospherical air before it is fitted for assimilation 

 and growth ; and though bloodless this air is no less necessary to the 

 growth and existence of polypes, which soon languish and die in ves. 

 sels of unrenewed water. Hence the current within the tubes of some 

 polypidoms which has been noticed : it is the movement of the nu- 

 trient fluid which has found its way from the alimentary sac to the 

 surface of the body, where it is subjected to that agent which alone 

 can fit it for the purposes of life. 



* Lect. Comp. Anat. in the Lancet, 1834, Vol. ii, p..959 — " All the cilia ap- 

 pear to commence and to cease their motions at the same moment. The con- 

 stancy with which they continue would seem to exclude the possibility of their 

 being the result of volition ; and they are, therefore, more probably determined 

 by some unknown physical cause, dependent, however, on the life of the animal." 

 Roget, Bridgew. Treat, i. 173. 



