202 Transactions of the Society. 



of tlie organism as shown in fig. 9, h, g, and in plate IX. fig. 7, and 

 is accompanied by an almost complete severance of the halves of 

 the nucleus as at li, fig. 9, plate VIII., which is then quickly effected ; 

 and the whole organism separates into two perfect forms as we 

 have before described.* When, however the fission is complete 

 the congested condition of the plexus-like structure at one end of 

 the nucleus is broken up by its diffusion, equally again, throughout 

 the entire hyaloplasm of the nuclear body as seen in plate VIII. 

 fig. 10, and in the next fission the same process is repeated. 



Now it is only in minute particulars that any of the four forms 

 before us differ from the mode of self-division here described. The 

 differences indeed are determined only by the peculiar way in 

 which the body-sarcode as a whole divides. In every case there is 

 a loss in one part of the nucleus of the plexus-like structure, and a 

 manifest thickening of it at other points of the nuclear body. 

 There is also either a beaded or otherwise irregular line — really I 

 believe a plate or disc — running along the entire line of cleavage of 

 the nucleus, and an opening of the two halves of the nucleus to 

 some small extent before the act of fission is participated in by the 

 sarcode of the general organism. In Folytoma uvella, for example, 

 the mode of fission differs from the above, by the fact that the 

 sarcode divides into two, four, eight, and sixteen separate forms 

 within the body- wall of the original organism.t In this instance 

 it is the middle of the nucleus that becomes homogeneous, and 

 the opposite ends that receive the plexus ; and the white line of 

 cleavage is exactly midway between them, as seen in plate VIII. 

 fig. 11. But in all important details, in describing the phenomena 

 in one, we have in effect described the behaviour of all these septic 

 nuclei in the act of fission. 



This will be instructively manifest in studying the larger 

 nucleus of Tetramitus rostratus. In plate VIII. fig. 12 we have a 

 drawing of this nucleus in the state in which it is arrested in 

 growth for the development of its internal structure. It is mag- 

 nified 8000 diameters, and the nuclear membrane or wall-like 

 investment is made manifest. In fig. 13 the plexus-like structure 

 of the whole interior of the nucleus is palpable ; and this is the 

 state in which it remains until just before the first indication of 

 the commencement of the fissional state has displayed itself in the 

 general substance of the body-sarcode. 



It will be remembered that the first sign that fission was about 

 to happen in the body was shown in the amoeboid condition of the 

 whole body of the monad, | as seen in plate IX. fig. 1. But by close 

 study of the nucleus this state is now seen to supervene upon an 



* Proc. Eoy. Soc, ibid. 



t Monthly Micr. Joiirn., xii. (1874) p. 261 et seq. 



X Ibid., X. (1873) p. 53 et seq. 



