or THE PROTOZOA. CILIATA. 355 



From the poriisal of this account, the thought arises, whether, instead 

 of proving- the existence and progressive development of internal ovules or 

 germs in the sense Perty adopts, it is not another illustration of embryo-de- 

 velopment by a sort of gemmation or breaking up of the nucleus, such as the 

 researches of Cohn, Stein, Lachmann and others have made known to us, and 

 concerning which we have now to speak {see Balbiani's researches, p. 329). 



The development of the nucleus into embryos takes place under different 

 circumstances and in a varied manner in different genera of Ciliated Protozoa. 

 It may occui' either without the previous encysting of the animalcule, or after 

 this process is completed. Again, in the latter condition, and without ulterior 

 change or metamori)hosis, either a few active embryos, or some encysted 

 germs, may be the result, or the whole nucleus may resolve itself into a 

 brood of monadiform beings, or, lastly, according to the views of Stein, the 

 encysted animal" may be metamorphosed into an Acinetiform being, out 

 of which embiyos are developed diverging in character more or less com- 

 pletely from the original ciliated Protozoon, to which, however, they eventually 

 recur. The development of embryos without the previous encysting of the 

 animalcule has been followed out by Focke, Cohn, and Stein in Nassida and in 

 Pammecium (Loxodes, Cohn) Bursaria (XXTIII. 10-14, XXIX. 28 to 34). 

 A portion of the nucleus is separated by fission or by an act of gemmation, 

 and constitutes a more or less orbicular body, in which a nucleus (XXIX. 34), 

 and then a contractile vesicle, shortly declare themselves (XXIX. 29). 

 Focke surmised that the so-called nucleolus originated this germ, which then 

 foimd, as it were, a lodgment and nutrition in the nucleus as in a uterus {see 

 Balbiani, p. 329) ; but Stein affirms that this body has nothing to do with the 

 origin of the germ, and is frequently to be seen separated and removed to some 

 distance from the nucleus (XXIX. 29). In appearance the disk-like germ is 

 finely granular, paler than the nucleus, and not surrounded, like the latter, 

 with a special membrane. Cohn represents it as existing in a distinctly 

 Hmited cavity, prolonged to the external surface as a tube or oviduct, and 

 terminated by a two-lipped orifice, through wliich the embryo makes its exit 

 (XXYIII. 11, 12). According to Stein, however, no such duct and external 

 orifice have an existence, except temporarily, dming the passage of the germ, 

 or germs when two or more follow in succession. This assertion of Stein 

 is supported by Cohn's o^vn observation, that the point of extrusion varied 

 in different indi^-iduals in its position, being at one time at the middle, 

 at another above it, at a thu'd below it, and, as the inile, on the left side, 

 although as an exception on the right side or even towards the anterior 

 margin. The act of birth occupies about twenty minutes ; and when the 

 embryo is about to escape, it exhibits a vibration on its surface, which causes 

 a motion in the surrounding water and hastens its detachment. This motion, 

 after continuing a short time, ceases, and the little being attaches itself to the 

 exterior of the parent (XXIX. 30). The chasm produced in the parent 

 during the extrusion soon closes up, and leaves no trace, except, it may be, a 

 slight hollow in the sm-face. The embryo has an elongated fissure, is rounded 

 at each end (XXIX. 30), and frequently rather contracted at its middle ; 

 internally it is finely granular and colomiess — not greenish, as Focke asserted — 

 and contains, besides a darker nucleus, one or two contractile spaces (XXYIII. 

 14). Cohn could discover no mouth ; but Stein displays in his figure an 

 oblique fold or groove (XXIX. 30), which may possibly rei)resent the oblique 

 funnel-like vestibule of the mature Paramecium. The vibratile movement 

 visible about the surface indicates ciliary action ; and if the embiyo be killed 

 ■with iodine, the presence of long cilia is demonstrated. StiU the most 

 peculiar feature in the new-bom animalcule is the possession of several soft 



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