ON THE PROTOPLASTID BODY, ETC. 327 



chief among which appear to be the nuclei. Now, in the 

 Ciliate Infusoria it has been shown by the elaborate investi- 

 gations of Maupas, and by the less complete, but in the 

 main confirmatory work of R. Hertwig, that the primary 

 object effected during conjugation of two individual ciliates, 

 is the transference of nuclear elements from cell to cell, the 

 process being accomplished in the following way. 



Previous to conjugation, the body of a Paramecium 

 contains, as I have said, two kinds of nuclear elements — 

 one large and more or less irregular, the other more 

 rounded and definite in form. The larger, or macro- 

 nucleus, remains unchanged, and takes no part in the 

 ensuing transference, but the smaller, or micro-nucleus, 

 goes through some extraordinary evolutions before the 

 conjugative act begins. After the animals become applied 

 together the micro-nuclei enlarge, and then elongate, the 

 chromatic substance streaming to the broader end (fig. 7-8). 

 Eventually both ends of the micro-nucleus become pointed, 

 and the micro-nucleus, now enormously elongated, bends 

 round upon itself in the manner represented in fig. 10, the 

 chromatic substance being massed along the concave side. 

 After a time, however, it again becomes rounded, the 

 chromatin becoming aggregated into an equatorial plate of 

 slender chromosomes, and the usual karyokinetic phases 

 are gone through in succession. This division of the 

 micro-nucleus is followed by another, so that there are 

 eventually four daughter micro-nuclei in each conjugate, as 

 the applied animals are called (figs. 11- 14). Three out of 

 these four daughter nuclei ^degenerate and disappear, and 

 the one which remains in each is that which happens to be 

 nearest to the oral aperture. These two remaining nuclei 

 now divide again, and the resulting nuclei remain connected 

 with one another with long filamentous strands (fig. 16), 

 strangely similar to the connecting spindle filament I have 

 elsewhere described in the divisions of sperm-mother cells 

 of the Cartilaginous Fishes. In each conjugate one of 

 the daughter nuclei remains nearer the oral aperture 

 than the other (fig. 16), and these two nearer ones approxi- 

 mate more closely, and come eventually to lie together 



