592 TRANSACTIONS OF SECTION D. 



fact that tlieir initial chambers are, at least in the great majority of cases, of 

 uniformly small size, a condition which I suspect to depend on their peculiar mode 

 of life. Again, in the simpler gi'oups {Gromiidce and Astrorkizidee) the covering 

 appears, in many cases at least, to expand with the growing protoplasm, so that 

 the evidence of their initial condition is not preserved in the shells. In these cases 

 also we have to seek for evidence of the course of the life-history in nuclear and 

 other characters. 



lievieio of Nuclear Characters. 



Turning now to the nuclear changes which ai-e found in PolystomeUa, there 

 are many features which are worthy of attention. In their feeding, locomotion, 

 and the mode of forming the shell, in fact in all that concerns their vegetative 

 existence, the megalospheric and microspheric forms are, so far as I am aware, 

 exactly alike; yet in one the economy is dominated by a single nucleus, and in the 

 other by many. Eichard Hertwig has compared a uninucleate organism, whether a 

 whole protozoon or a metazoan cell, to an absolute monarchy, and the multi- 

 nucleate organism to an oligarchy, in which the rulers, though many, perform 

 identical functions. In the life-history of PolystomeUa the apparently revo- 

 lutionary change in government occurs at each reproductive phase, yet the internal 

 and external relations of the state, as far at least as its vegetative life goes, appear 

 to remain unaltered. Why the nucleus of the microspheric form should divide up 

 into a number of daughter nuclei, while that of the megalospheric form remains 

 single, is, to me at least, entirely obscure. 



The separation of portions of the chromatic substance of the nuclei, in both 

 forms of the species, and the ultimate resolution of the whole of it into such 

 shreds, dispersed through the protoplasm, appeared at first a puzzling and obscure 

 phenomenon. In metazoan cells, which are advancing to the formation of the 

 reproductive elements, the nuclear divisions occur in regular succession, and the 

 nucleus of a germ-cell may be regarded as the daughter nucleus, granddaughter, 

 great-granddaughter, and so forth, of some other nucleus which went before it. 

 The aphorism OHi?;is nucleus e nucleo appears to hold good for the metazoa, 

 but how does it find its application in the case we are considering? Is there 

 any recognition of the hereditary principle when the change of government of 

 our state occurs ? Light has recently come on this obscure phenomenon, and, 

 as usual, by the results obtained in otlier groups of Protozoa. In the introduc- 

 tory essay, Die Protozoen und die Zellthcorie, which he contributed to the first 

 number of Schaudinn's ' Archiv ' Richard Hertwig drew attention to morpho- 

 logical elements of the protozoan body, distinct from the protoplasm on the one 

 hand a,nd from the formed nucleus on the other, and applied to them the name 

 chromidia. They consist of groups of granules or branched strands of a sub- 

 stance staining with the same reagents as the chromatin of the nucleus. In 

 Actinospkeerium, in which Hertwig first recognised them, they are normally 

 present in the protoplasm, but their number is increased in particular states of the 

 body in relation to metabolism, as by over-feeding, but also, it was found, by 

 starvation. The chromidia are derived from the nuclei, and indeed under certain 

 circumstances the nuclei may completely resolve themselves into chromidia. A 

 structure present in the body of many shelled Rhizopods, and regarded by Hertwig 

 as of the same nature as the chromidia, is the chrotnidial net. In Arcella this 

 lies in the peripheral parts of the disc-like body, and sends reticulate processes 

 into the rest of the protoplasm. Like the chromidia it stains with chromatin 

 stains. Hertwig concludes that in Arcella the two or three nuclei originally 

 present may, in a certain phase of the life-history, completely disappear, and that 

 in that case nuclei are formed afresh by the aggregation of chromatm material 

 about new foci in the chromidial net.^ A similar chromidial net was described by 

 Hertwig in Echinopyxis. In the following year Schaudiun * pointed out that the 



' R. Hertwig, ' Ueb. Encystierung u. Kernvermehrung bei Arcella vulgaris,' 

 KupEEer's Festschrift, 1899. 



= ' Untersuchungen iib. d. Fortpflanzung einiger Rhizopoden,' Arh. aits d. Kait. 

 Gesundheitsamte, Bd. xix., Heft 3, 1903. 



