igoy.] Records of the Indian Musetnii. 67 



to become stationary on the sides rather than at the bottom of the 

 aquarium, unless they are given empty shells, in which they ensconce 

 themselves at the bottom. 



Both forms possess considerable powers of progression, but they 

 do not habitually move in the same way. The only method I have 

 seen the typical form adopt is that observed by Stoliczka viz., by 

 crawHng slowly on the basal disk along a vertical or horizontal sur- 

 face. This method of progression is effected partly by alternate 

 contractions and expansions of the disk, and partly by a copious 

 secretion of very tenacious mucus from the glandular cells which 

 abound on this disk and round the base of the column. It is a slow 

 and feeble one, as it generally is in Actinians ; Stoliczka records that 

 a specimen in his aquarium moved 7 inches in 24 hours, while one in 

 mine took three days and nights to move half the distance. 



Possibly the young of the pond race may adopt the same 

 method of progression occasionally, but as a rule they drag them- 

 selves along by their tentacles — a much more rapid method. A ten- 

 tacle is stretched out to its greatest length, until it becomes fila- 

 mentous. Some part of its surface is then applied to a fixed object, 

 and a gland cell in the neighbourhood secretes a drop of mucous 

 secretion, which fixes the tentacle to the object. The tentacle thus 

 fixed contracts, dragging the whole animal forward as it does so ; 

 the strain on its surface being considerable, the cells in the neigh- 

 bourhood of the gland are drawn out into irregular projections at the 

 points at which the}^ are held by the mucus. Latel}' I have ob- 

 served the same phenomenon in the tentacle? of Hydra, and I have 

 little doubt that this is the true explanation of Zykoff's statement 

 that the ectoderm cells of the tentacles of Hydra put out pseudopo- 

 dia which are used in progression {Biol. Centralhlat., xviii, p. 272, 

 i8g8). When the tentacle is dragged away after a forward move- 

 ment of the organism, the false pseudopodia naturall}' appear in an 

 exaggerated form ; the}^ are not due directl}" to movements of the 

 protoplasm of the cells, but to a mechanical strain on the external 

 surface of these cells. I have been able to observe this method of 

 progression in the case of very young individuals of the Actinian 

 under a fairly high power of the microscope. Although the tentacles 

 play in it the most important part, the walls of the -column are also 

 adherent to the surface along which the animal is travelling, and if 

 it is moving vertically up the walls of an aquarium, as I have 

 occasionally observed it to do, the ''suckers" can be seen to be 

 applied to the glass very closely. They do not appear to be at all 

 markedly concave on the surface, however, as would be the case if 

 they actually functioned as suckers. 



In addition to this mode of- progression with the aid of the 

 tentacles and the surface of the column, individuals of the variety 

 exhibit, at all ages, strongly marked muscular movements of the col- 

 umn wall. It is evident that the separation of the circular muscle of 

 this region into separate circular strands is physiological as well as 

 anatomical, for it is possible for each strand to contract independently 

 of the others, so that the column appears just as though an extremely 



