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Show 18 ON CLASSIFICATION. of an el ongat ed Oval Sha<- pe (Fioo· . 4, A B d), whic.h .h as .b oen called the "nucleus," though it must be c~refully d_tshnguiShe.d f th " cleus" of a cell. Upon one side of th1s, and, as 1t rom e nn d (F' 4 n I . ·t ck on to it is a little rounded bo y Ig. , d), wme, s u ' 1 I " Tl · wh I.c h 11 as rec e1'v ed the name of the "nne eo .u .s . 1e animal SW·i mS a b OUt , di·I·ven by the vibration of its . cilia, and w. hatever nutriment may be floating in the water Is a~propn~.tAd by means of the current which is caused to set continually Into the short gullet by the cilia which line that tube. . But it is a singular circumstance that these animals have an 1. entary canal consisting of a mere gullet, open at the bottom, aim · d' and leading into no stomach or intestine, but op.e:1Ing 1rectly . into the soft central mass of sarcode. The nutntious matters passing down the gullet, and then into .the central n::or~ fluid. substance become surrounded by spheroids of clear hquid (F1g. 4, A d), ~onsisting apparently of the water swallowed wit~ ~hem, so that a well-fed Parammcium exhibits a number of cavities, each containing a little 1nass of nutritious particles. Hence formerly arose the notion that these animals possess a number of stomachs. It was not unnaturally imagined that each of the cavities in question was a distinct st_omach ; but it .has since been discovered that the outer layer of the sarcode Is, by means of some unknown mechanism, kept in a state of constant rotation ; so that the supposed stoinachs may be seen to undergo a regular circulation up one side of the body and down the other. And this circumstance, if there were no other arguments on the same side is sufficient to necrative the supposition that the food- ' 0 . co:o.taining spaces are stomachs; for it is impossible to imagme any kind of anatomical arrangement which shall permit true dilatations of an alimentary canal to rotate in any such manner. Frecal matters are extruded from an anus, which is situated not far from the mouth, but is invisible when not in use. It is an interesting and important character of the Infusoria, in general, that, under some circumstanees, they become quiescent and throw out a structureless cyst around their bodies. The Injusorium then not unfrequently divides and subdivides, and, the cyst bursting, gives rise to a number of separate Infusoria. The ren1arkable powers of multiplication by fission and GREGARINIDA, RHIZOPODA, SPONGIDA, AND INFU ORIA. 19 gemn1ation which many of th group exhibit ar well known; but within tlte la t few year the investigations of Mi.ill r, Balbiani, Stein, and others, have shown that these minute creatures possess a true process of sexual multiplication, and that the sexual organs arc those which have bceu denominat d 'nucleus" and ''nucleolus." 'J.1he nuclens i the true ovarythe nucleolus, the testis, in Parammcium. At particular times, the latter increases very much in size, and it substance i broken up into rod.like bodies, which repr sent sp rmatozoa. Two Inf~tsoria, in this condition, becmne conjoined, and the nucleolus (now C•)nverted into a spennatic cap.,ule) of ach pas es into the body of the other. ~rhe spennatic filaments are said to enter the nucleus, which then enlarges, and ~ither divides into, or gives off, a number of rounded germ , which b come oval ciliated bodies provided with long procc ses. These make their way out of the body, and, it js believed, are metamorphosed directly into young Parammcia. But, perhaps, further information is required before we can be quite certain on this point. |
