1872.] 



Modes of Origin of Infusoria fyc. 



263 



fission of some smaller portion of the embryo-mass. Sometimes it was the 

 largest embryos which were observed to undergo this process of fission, 

 though the phenomenon was by no means confined to them *. 



On emerging from the cyst, all the embryos, although differing somewhat 

 in size, were of the same shape. This closely corresponded with the de- 

 scription given of Paramecium kolpoda in Pritchard's ' Infusoria,' namely : 

 — " Ovate, slightly compressed ; ends obtuse, the anterior attenuated 

 and slightly bent like a hook." Cilia existed over the whole body, though 

 they were largest and most numerous about the anterior extremity. No 

 trace of an actual buccal cleft could be detected ; and (except in the posterior 

 portion of the body, where a large and very persistent vacuole was situated) 

 the organism was everywhere densely packed with the large, homogeneous, 

 biscuit-shaped particles. For many days these most active Infusoria seemed 

 to undergo little change, though afterwards the number of the contained 

 particles gradually began to diminish, whilst the body became more and 

 more regularly ovoid, and a faint appearance of longitudinal striation 

 manifested itself, more especially over its anterior half. At the same time 

 a very faint and almost imperceptible mass ("nucleus") began to appear 

 near the centre of the organism ; and when examined with a magnify- 

 ing power of 16/0 diameters, a lateral aperture (mouth) -g^s" m diameter 

 was seen, which was fringed by short active cilia, arranged like the spokes 

 of a wheel. These peculiarities correspond very closely with those of an 

 embryo Nassula. Very many were seen with similar characters ; and mul- 

 titudes existed in all conditions intermediate between this stage and that 

 of the simpler organism which first emerged from the cyst. No further 

 stages, however, could be watched, as at this time some change took place 

 in the infusion which proved fatal to all the free Infusoria and also to the 

 multitudes of embryos which were at the time developing in the pellicle ; 

 these became more minutely granular and opaque, their movements ceased, 

 and the cyst-wall grew thicker. This phase of development disappeared, 

 therefore, almost as suddenly and mysteriously as it had appeared. The 

 cysts were examined from time to time for many weeks afterwards, but they 

 seemed to undergo no further change f. 



It will, of course, be seen that the phenomena which I have described 



* Partial desiccation has a strong tendency to induce such fission, as I found by the 

 frequency with which it occurred when the water had in great part evaporated from 

 specimens placed in a developmental chamber. Fission of Pen /'till i ion-filaments (into 

 conidia), and also of encysted Eughnce, have several times been seen under similar cir- 

 cumstances. 



t In a maceration which was subsequently made during very cold weather, when the 

 temperature of the room, even during the day, was rarely higher than 53° F., large 

 Amoebae, visible to the naked eye, some of which were -ysu" diameter, were produced 

 from the pulpy under portions of the pellicle. They formed great masses of living 

 granular jelly of the simplest description — too large to move as a whole, though fluxes 

 of portions of their semifluid body-substance were continually taking place in different 

 directions. 



v 2 



