184 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



plasm in Infusoria corresponds with that in Metazoa, and we 

 are justified in transferring to these Protozoa the conceptions 

 at which we have arrived as to the relation and significance of 

 the Metazoan idioplasm, and, above all, the conception of the 

 individual difference of nuclear idants. 



R. Bergh's researches upon Urosfyla grandis prove that the 

 spindle of the micronucleus contains, during division, nine rod- 

 like idants (see his fig. 9). Since, however, only one side of 

 the spindle is represented in the drawing, the total number of 

 idants must be eighteen. All who have observed the phenomena 

 of conjugation agree that the first preparator}^ change in the 

 micronucleus consists in a considerable enlargement^. Maupas^ 

 gives a series of fourteen figures illustrating this increase in 

 the size of the micronucleus and its conversion into a spindle, 

 and he calculates that, during this period, its original mass is 

 multiplied eight-fold. 



Richard Hertwig ^, who has directed special attention to this 

 point, found that the micronucleus of a Paramaecium, imme- 

 diately after division, was extremely small, — less than three 

 microns* in diameter, while that of the micronucleus of an 

 animal previous to conjugation was about seventy-five microns. 



This enormous increase in size largely depends on the growth 

 of the achromatin substance which plays a most essential and 

 remarkable part in the subsequent divisions, but it does not 

 therefore follow that there is no simultaneous increase in the 

 idioplasm. I assume that the increase of the micronucleus is 

 connected with a doubling of the idants by longitudinal division. 

 There is at present no proof of this assumption ; for no one has 



' Schewiakoff's beautiful observations (' Ueber die karyokinetische 

 Kerntheilung der Englypha alveolata ; ' Morpholog. Jahrbuch, Bd. XIII. 

 p. 193 ; 1888 ), show that the Infusoria are not the only Protozoa possess- 

 ing idioplasm in the form of idants. Not only are idants (chromatosomes) 

 shown to exist in the form of loops, but their behaviour during karyo- 

 kinesis is so accurately described as to leave no doubt that an ' equal 

 division ' is its outcome. The longitudinal splitting of the loops was 

 observed not only in microscopic preparations, but in the Hving animal 

 in the act of dividing. It is clear that Eiiglypha is well adapted for 

 observation, and it would be of great value to investigate the relations of 

 its nucleus during conjugation from the standpoint of this essay. 



- Maupas, ' Le rajeunissement karyogamique chez les Cilies. ' Archives 

 de Zool. exper. et gen. 2 ser. Vol. VII. PI. IX. Figs. 1-14. Paris, 1890. 



^ R. Hertwig, ' Ueber die Conjugation d. Infusorien.' Munich, 1889. 



■* A micron or ix is the ^-^^-^ of a millimetre. 



