246 Dr. T. Williams on the Mechanism of Aquatic 



ends of the tentacles : they are not perforated at their distal 

 extremities. In Hydra viridis aud H. fusca, by means of the 

 rolling granules, the fluid may be readily detected by the eye. 

 It cannot be renewed directly from without. It is replenished 

 through the walls of the stomach {b). The respiratory is here a 

 function distinct and separate from the digestive. A living cor- 

 pusculated fluid is submitted to the influence of the surrounding 

 medium, by aid of the tentacles. These appendages in the 

 hydraform zoophytes are furnished neither within nor without 

 with motive cilia. They maintain the flux and reflux motion of 

 the embraced fluid, in virtue of the contractile endowments of 

 their parietes. In the second variety, illustrated by the sea-ane- 

 mone (fig. 3, b), the open interval between the stomach and the 

 integuments, though partitioned by dissepiments, is very capa- 

 cious. The hollow axes (c) of the tentacles are continuations, 

 in all species, of the perigastric space. They are filled with 

 the same fluid as the latter. In some species of Actinia, the 

 tentacles are perforated at the extreme ends : Anthea Cereus is an 

 example. In the greater number they are csecal. The interior 

 of the tentacles, in common with the perigastric chambers, in all 

 species are richly ciliated {d) . The exterior of these appendages 

 in many instances is covered only by an ordinary uon-vibratile 

 epidermis. The chylaqueous fluid* is an inferiorly vitalized 



* Under this term (see Phil. Trans. 1852), the author has ventured to 

 distinguish the fluid which occupies the gastric and perigastric cavities of 

 all animals below the Annehda. He has elsewhere endeavoured to prove 

 the proposition, that in all animals below the Echinoderms, it constitutes 

 the exclusive nutritive fluid of the organism ; that in those families, as in 

 Zoophytes and inferior Echinoderms, in which it is readily ejected fi'om the 

 body and as reaihly replaced, it is very little removed in composition from 

 salt water, and corpusculated only in a slight degree. It is simply al- 

 buminized sea water. But it has already undergone such preparation as 

 fits it to enter the " protean " cells of the solids. Here, as illustrated in the 

 examples of the Amceba and Sponge, it assumes a more highly vitahzed and 

 corpusculated chai-acter. It may be said that in the cells it is true blood, 

 in the visceral cavity chylaqueous fluid. The difficult problem of respira- 

 tion in the lowest forms of animal life can be solved only by determining 

 the real stages through which the fluids pass in the processes of animahza- 

 tion. If the great mass of the chylaqueous fluid contained in the polypedal 

 and visceral chambers consist of pure, unvitahzed, unalbuminized sea water, 

 then the tentacles can subserve no respiratory purpose ; since between two 

 fluids (that within, and the element without the tentacles), of identical com- 

 position and specific gravity, there can occur no interchange of gases. But 

 if, on the contrary, to this great reservoir of fluid be assigned the value of a 

 chylaqueous compound, though it may have undergone only the first and 

 lowest grade of assimilation, then the entire mechanism of respiration and 

 nutrition becomes intelligible. This argument enforces the ])hysiological 

 ])rinciple, which, in order to demonstrate the true seat of the aerating pro- 

 cess, demands that the real constitution of the fluids be Jirst discovered. 

 In studying the nutritive and respiiatory actions in all invertebrate animals. 



