STRUCTURE OF ACTINOPHKYS. 15 



the captured animalcule is lying slowly retracts, and forms at first a 

 shallow depression, in which the prey, apparently adherent to the sur- 

 face and following it in its retraction, is finally lodged. The depres- 

 sion, by the continued retraction of the substance, becomes deeper ; the 

 imprisoned animalcule, which up to this time had projected from the 

 surface of the Actinophrys, entirely disappears within it, and at the 

 same time the tentacula, which had remained with their extremities 

 applied to each other, again erect themselves and stretch out as before 

 the capture. Finally, the depression assumes a flask-like shape by 

 the drawing-in of its margin, the edges of which coalesce, and thus a 

 cavity closed on all sides is formed wherein the prey is lodged. In this 

 situation it remains a longer or shorter time, gradually, however, 

 approaching the central portion of the body. In the mean time the 

 periphery of the Actinophrys regains in all respects its pristine condi- 

 tion. The engulfed morsel is gradually digested and dissolved, as is 

 readily seen by its change of appearance from time to time. If entirely 

 soluble, as, for instance, an Infusorium, the space in which it is con- 

 tained contracts as the dissolution of its contents goes on, and finally 

 disappears altogether : should there, however, be an indigestible residue, 

 a passage for its exit is formed, and it is expelled by renewed contrac- 

 tions of the homogeneous substance, and in the same direction, or 

 nearly so, as that which the morsel followed in its introduction. The 

 passage and the opening through which the expulsion was effected dis- 

 appear again without leaving a trace. 



(32.) The number as well as the size of the morsels taken at one 

 time, in the manner above described, by an Actinophrys, is very various. 

 Sometimes there may be two, four, or six swallowed simultaneously ; 

 occasionally more than ten or twelve. 



(33.) A remarkable contractile vesicle is always visible in these ani- 

 malcules, which Mr. Weston* regards as a valvular orifice. It is best 

 distinguished when about the edge of the seeming dislc, and is never 

 still night nor day, being slowly but without cessation protruded, occu- 

 pying from ten to seventy or eighty seconds in its development, and 

 then, like the bursting of a vesicle, rapidly and totally subsiding : for 

 an instant it totally disappears, but only to be as gradually and as 

 certainly reproduced. Should that side of the creature where the valve 

 is placed be turned from the observer, the effects of the contraction are 

 distinctly seen, although the valve itself is not ; for at the instant of its 

 bursting and closure, some half a dozen or more of the tentacles situated 

 on or about it, which have been gradually thrust from their normal 

 position by the act of its protrusion, now approach each other with a 

 jerk-like motion caused by the sudden bringing together of their bases. 



(34.) The valve seems to be formed of a double layer of the external 

 hyaloid membrane, the edges of which appear to adhere to each other 

 * Quarterly Journal of Microscopical Science, vol. ir. p. 116. 



