THE ANATOMT OF ALCYONIUM DIGITATUM. 381 



This appears to be the case from the following considera- 

 tion : — The dorsal mesenterial filaments of the primary, i. e. 

 the oldest, polyps of the colony extend right down to its base; 

 and, so far as I could observe, there is no diminution of the 

 vigour of the current produced by them in the lower regions 

 of the tube. If there is a current of water in one direction at 

 the side of a tube which is closed at one end, it is obvious 

 that there must be a current in the reverse direction on the 

 opposite side. The endoderm of the lower parts of the tube, 

 although provided with large intercellular spaces as described 

 above, is nevertheless living and active. (In Tubipora and 

 Clavularia viridis the endoderm dies in the lower ends of 

 the tubes.) I have no doubt, then, that the endoderm of all 

 parts of the ceelenteron can and does absorb nourishment in 

 the fluid form. 



There is no evidence that particles of food are taken up in 

 the solid form by the endoderm of Alcyonium. I have not 

 been able to observe any solid particles of food other than 

 the nutritive spheres in any of the endoderm-cells I have 

 observed, either in sections or in teased preparations. I have 

 seen no diatoms or other unicellular algae or fragments of 

 animals embedded in the endoderm. Particles of carmine 

 suspended in the water are, however, readily seized by these 

 cells wherever they occur; and in some cases I have seen 

 them embedded in the cells of the mesogloea, indicating that 

 they may be handed on from cell to cell throughout the 

 system. 



Literature. 



1. Bastek, Job. — ' Natuurkundige Uitspanningen,' eerste deel, p. 26, 1762. 



2. Berkenhout, J. — ' Synopsis of the Natural History of Great Britain 



and Ireland,' i, p. 212, 1795. 



3. Bosc, L. A. G. — ' Histoire naturelle des Vers,' iii, p. 151, 1827. 



4. Couch, J. — ' A Cornish Fauna,' vol. iii, p. 58, pi. xiii, 1, 1844. 



5. Danielssen, D. C. — ' Norske Nord-Havns' Expedition, Alcyonida,' 1887. 



6. Ellis, J. — 'Essai sur I'Histoire naturelle des Corallines, &c.,' 1756. 



