204 Transactions of the Society. 



of these is Tetramitus rostratus. When followed into the mature 

 state from the germ it speedily exhibits the early nuclear symptoms 

 of fission, and the process of division goes on in the one of the 

 divided forms that we can follow, after each successive division, for 

 from six to eight hours. In each act of fission an amoeboid condi- 

 tion is set up, as we have seen, in the body-sarcode. But the 

 organism retains its power to swim. When, however, the last link 

 in the chain of fission has been reached, the organism that consti- 

 tutes that liak becomes an amoeba almost entirely, as seen in plate 

 VII. fig. 9, retaining only the characteristic forepart of the body, 

 with the four flagella a. But it does not swim ; precisely like an 

 amoeba, it progresses by pseudopodia.* There are always several 

 such in a field of some age, and they are, apparently by accident, 

 constantly coming in contact with each other as they creep, with 

 the peculiar result that their respective sarcodes almost directly fuse 

 into each other, until nucleus reaches nucleus and the two nuclei 

 melt " either into other," and the whole of the blended bodies become 

 a globular sac, which ultimately emits an enormous mass of germs. 



For years we had been struck with the enlargement of the 

 nucleus in forms that had entered this stage (plate VII. fig. 9) 

 previous to blending. But I have now made out that the final 

 fission form may be known and identified, before the strong amoeba- 

 like change arises, by a close study of the nucleus ; which instead 

 of passing from the stage seen in plate VIII. fig. 17, to that seen in 

 fig. 18, ibid., gradually loses aU trace of plexus-like structure every- 

 where, and becomes greatly enlarged, with a milky aspect, and in 

 this condition it is unafiected by the acetic methyl-green. It 

 is in this state of the nucleus that the organism ceases to swim, 

 and if brought into contact with another in the same state fuses 

 the general sarcode with it, almost as though two globules of 

 mercury had touched. A figure of the act of blending is given at 

 plate VII. fig. 10, where the nuclei are almost in contact ; directly 

 such contact is effected there is a distinct fusion, but no trace of 

 structure can be seen anywhere throughout the blending nuclear 

 bodies. Every artifice and device that could be tried, every method 

 of illumination, and the employment of reagents, failed to reveal 

 anything but the almost dazzling white substance as a whole of the 

 nuclear bodies. Beale's carmine evenly and delicately tinted the 

 nuclei, but that was all. 



The blending is effected with varying rapidity, but is always 

 quickened directly the two nuclear bodies are in actual contact 

 with each other, and from that time the amoeboid condition becomes 

 less and less marked, until it wholly ceases, and we have a relatively 

 large oval sac, extremely white, and although diaphanous, still not 



* Monthly Micr. Journ., x. (1873) p. 53 et seq. 



