I 



Respiration in Invertel/rate Animals. 245 



pendent organism. The included fluid, moved by the slow con- 

 traction of the cell- membrane, is a granulated, nutritive com- 

 pound. That diffused between the cells, in composition, 

 is less removed from the standard of sea-water. The latter re- 

 plenishes the former. The inorganic fluid, entering from with- 

 out into the interior of the living-cell-tissue, carries with it in 

 solution a large amount of atmospheric air. In these lowly 

 organisms, this dissolved air probably suffices to oxygenize their 

 simple fluids. As the contained flmds are rapidly renewed, the 

 nutritive and the respiratory process come to be performed by 

 one and the same act. This is the history of the breathing 

 function in the Rhizopoda and in Actinophrys Sol, recently 

 described by KoUiker*. The superficies of the whole gelatinous 

 cortex of the sponge is overspread by a film of ciliated epithe- 

 lium. It has now been proved by Dr. Dobief and Mr. Bower- 

 bank, that the " currents " of the sponge are due to the agency 

 of these motive organules. These currents are simultaneously 

 nutritive and respiratory. 



Polypifera. — Three varieties of plan, in the mechanical condi- 

 tions of respiration, prevail among Zoophytes : the Hydrafm'm 

 (PI. XII. fig. 2), the Actiniform (fig. 3), and the Asteroid polypes 

 (fig. 1) exemplify three minor forms of one type of structure. 

 In the first the space between the stomach and the outer limit 

 of the body (fig. 2, a) is subdivided by the intersection of delicate 

 tissue into areolae, iu which the fluid to be aerated is contained J. 



The fluid penetrates along an axial channel to the furthest 



* See Quarterly Journal of Microscopic Science, Oct. 1852. 



t See Annals of Anatomy and Physiology, No. 2, May 1852. 



X The author has stated in the text the impression which he has derived 

 from numerous ohservations on the common hydra of our pools, that the 

 tentacles open into the perigastric areolse, as shown at (a) fig. 2, and not 

 into the stomach, and that they are tubular, not sohd threads, as shown at 

 (6) fig. 1. If, as recently stated by Prof. AUman (Proceedings of the Royal 

 Society, May 31st, 1853), they open directly into the stomach, the tentacles 

 can only be injected by the contents of the latter, and their function would 

 partake of a digestive as well as a respiratory character ; and further, the 

 digestive system of the hydra would conform with the medusan type which 

 is marked by the direct extension of canals from the stomach, and by the 

 absence of a splanchnic cavity, the stomach being merely an excavation in 

 the solid parenchyma of the body. The observations of Prof. Allman were 

 instituted on Cordylophora, a genus of Tubulariadce. According to my 

 researches very lately made on Tubularia indivisa and Alcyonium, the ten- 

 tacles are tubular and open into the perigastric chambers, which they equal 

 in number. From its interest, this question cannot remain long unanswered. 

 If in the hydraform and tubularian zoophytes the tentacles are prolongations 

 of the stomach, properly so called, zoophytes, as a class, might be ranged 

 under two leading divisions; that 1st in which the tentacles are gastric, and 

 2nd that in which they are perigastric prolongations. The fluids would 

 admit of a similar division. 



