260 GENERAL HISTOEY OF THE INFUSORIA. 



The tentacula are moveable and retractile, the divergent bundles may be 

 collected into parallel groups, and di-awn inwards, with the protruding sup- 

 porting lobes, to a greater or less extent. Stein aifirms that, in the first stage 

 of development, Acinetce have no tentacula. 



The body of an Acineta, within the capsule or external integument, con- 

 sists of soft colourless sarcode, rich in granules, fat- corpuscles, and minute 

 globules. It is enveloped by an elastic yielding membrane, which becomes 

 most distinct when the body shrivels mthin the capacious cavity of the 

 capsule (XXIII. 3, 6, 8). The body appears in some Acinetce capable of 

 extending itself above the capsule, which must therefore be fissured in front, 

 in the form of a tongue-hke process (XXIII. 17, 18, 19). A finely granular 

 and opaque nucleus is always distinguishable in the interior, usually near the 

 centre. Its shape is very varied, and may be oval, ovoid, clavate, reniform, 

 band-like, vermiform, or horse-shoe shaped (XXIII. 1, 6, 17, 22). In a 

 few examples, e. g. of the supposed Acineta of Opercularia, it is much and 

 irregularly branched (XXX. 3, 4). The addition of dilute acetic acid is a 

 ready and efifectual means of bringing the nucleus to hght, and of demon- 

 strating its enclosing sac ; and as it is more solid and compact than the 

 contents around it, it may now and then be separated by crusliing the Acineta. 

 The nucleus is enveloped by its peculiar membrane ; a fact which becomes 

 e\'ident in sevei^al cases by the apparent double line surrounding its gra- 

 nular mass (XXIII. 6-22). In a few instances, moreover. Stein has de- 

 scribed a contractile space witliin the nucleus, e. g. in that of Opeixularia 

 berberina. 



Xot unfrequently the nucleus looks as if double, or as sending ofi* a process 

 from itself; a critical examination of such specimens has convinced Stein that 

 the ofi'shoot is the commencing development of the germ or embiyo of the 

 Acineta (XXIII. 7, 8, 19). This he has proved by watching the nucleus 

 through all its intermediate stages, from a simple ovoid or elongated figure 

 until the embiyo has gro^Ti and separated itself from it prior to its escape 

 from the Acineta. The nuclear appendix, when separated, is found to have 

 an enclosing membrane, which ultimately surrounds the embiyo like a sac, 

 and admits of a certain degree of movement within it (XXIII. 4, 5). 



Another distinct organ of Acinetina is the contractile vesicle. Usually one 

 only is present ; but in some instances two, and more rarely three or more, 

 make their appearance (XXIII. 1, 5, 21). Xear the external margin a series 

 of clear vesicular or vacuolar spaces presents itself, as in the Diademiform 

 Acineta (XXIII. 15, 16) ; such, however, present no rhythmical contractions, 

 and cannot be regarded as true contractile sacs. The embryos developed 

 from Acinetw are likewise furnished with one, and occasionally mth two, of 

 those organs (XXIII. 2, 4, 5, 15, 27). Excepting the embryos or germs, no 

 other special structures are seen amid the granular contents of Acinetina. 

 Alimentary vacuoles and particles of food or other matters derived from with- 

 out never make their appearance ; for the body, even if not entii'ely enclosed 

 within the shut sac or capsule, is covered with an integument, and has no 

 sign of a mouth for the admission of food. Yet Acineta; generally have the 

 power of nourishing themselves, by the medium of their tentacula, which 

 appear to act as suckers, di'awing in by endosmosis the nutrient juices from 

 the animalcules which get entangled by them. 



If Stein's details be correct, some Acinetiform beings would appear to have 

 no power of self-nutrition ; for their substance is described as gradually used 

 up in the formation of germs, and this decrease to be followed by a shrinking 

 or collapse of the capsule, but at a comparatively slower rate. Tliis phe- 

 nomenon is illustrated by Stein in the Acineta ascribed to Vaginicola 



