OF THE PROTOZOA. ACTINOPHRYINA. 245 



layer or skin, is a somewhat iirmer or more condensed tissue than that sub- 

 jacent. 



The Actinophryina are composed of a homogeneous elastic sarcode, occupied 

 by granules in varying number, and by vacuolae. The granules are especially 

 accumulated in the centre, to wliich they consequently impart a greater opacity 

 and deeper colour. Hence several authors have spoken of a central medullary 

 mass surroimded by a clearer cortical lamina (XXIII. 28, 29). Still there 

 is no natural separability into two such portions ; for their relative size varies 

 according to the supply of food received. Dr. Strethill Wright (in a letter) 

 proposes to apply the unexceptionable terms " endosarc " and " ectosarc " to 

 the medullary and cortical portions respectively. The contained granules are 

 rounded, opaque, and, for the most part, of a fatty character. The granules 

 are less abundant in the ectosarc ; but those of a finer sort are seen in smaller 

 numbers even in the lower end of the filaments, and Lachmann (A. N. H. 

 1857, xix. p. 223) asserts that he has seen their motion there, as well as in 

 the general substance of the body. Mr. Weston also remarks {op. cit. p. 122), 

 *' With a -i-th objective I can distinctly see granules in constant motion in the 

 body of the ActinopJirys, similar to those always found in the points of Clos- 

 terium Lunula.'''' The vacuoles occur both in the cortical and medullary 

 portions, but are smaller in the latter, and they never penetrate into the 

 substance of the filaments. 



At first sight, as Kolhker notices, the tissue appears delicately ceUular : a 

 closer inspection, however, shows that this is not the case ; for on pressure 

 being made, a coalescence into larger, or, otherwise, a subdivision into smaller, 

 areolae is the consequence (XXIII. 28, 29, 30). 



The tentacles or filaments give to the Actinophryina their most distinctive 

 features. They are usually pretty regularly and uniformly distributed over 

 the entire surface, and in figure taper from the base to the apex, which is 

 sui^mounted by a rounded knob. Unlike other observers, Cienkowsky {J. M. S. 

 1857, p. 101) represents the capitate form to be exceptional, and that the 

 rule is for the filaments to taper like setae. Dujardin, by the way, appears to 

 have thought the capitate extremities accidental ; for he describes the filaments 

 as often becoming globular in the act of contraction. In smaller specimens 

 the filaments exceed the diameter of the body in the length, but in larger 

 ones are not more than equal to, or are even less than, it. In the same 

 species their number and position are tolerably constant. In composition, 

 the tentacula are processes given off from the sarcode mass, and are destitute 

 of an integument, as proved by their power of coalescence when approximated. 

 They are retractile, and can be withdi^awn into the common mass ; they can 

 also be dii-ected towards dififerent sides, and curved upon themselves. Perty 

 states that they can assume so rigid a condition that other animalcules some- 

 times impale themselves upon them ; this statement is nevertheless uncon- 

 firmed, and, indeed, seems scarcely probable. KoUiker (op. cit. p. 31) speaks 

 of the filaments as undergoing various changes of form, '" such as elongation, 



shortening, local sweUing, bending, &c It is especially interesting to 



observe that the filaments, singly or together, frequently disappear entirely, 

 entering at last, as it were, by continued retraction, into the substance of the 

 body, leaving no trace of their former existence .... whether the filaments 

 which disappear are always reproduced in the same spot is not determined ; 

 i-n some instances this did not appear to be the case, although in every 

 instance the number and position of the filaments is pretty constant " — unlike 

 the variable processes of Amoeba. Ehrenberg assigned to the tentacles, 

 among other purposes, that of organs of progression ; direct observations are, 

 however, wanting to prove this purpose, and both KoUiker and Stein are 



