A critiral study of the cytology of Crepis virens. 
127 
The ScHREiXERS (50) have checkcd the action of different fixing 
fluids on the resting spermatogoiiial niiclei of Mijxine glutinosa. They 
found that, fixed in Herilvxx’s formula, the chromatic contents of the 
nncleus were distribiited as “feine Chroniatinkörnchen, die hie und da 
zn etwas größeren gesammelt sind” (p. 197), (50, PI. 6, fig. 3 a), whereas 
fixed in a chromo-snbliniate solution (Zexker) “sieht man nie eine 
so feine Verteilung des Chromatins. Es zeigt sich hier zu gröberen 
Klumpen und Fäden gesammelt” (p. 198), (50, PI. 7, figs. 17 a and i). 
The evidence afforded by the observations and experiments ennme- 
rated above, strongly snggests that the definite aggregations of chromatin 
which are visible in some resting nuclei are inerely the expression of 
chromatic concentration, and do not represent ‘pro-chromosomes’ in the 
strict sense of that term. Kot only has it been shown that the degree of 
precipitation may be modified experimentally by the action of different 
fixing formulae, and by the control of their penetration, bat also that 
nuclei, though subjected to precisely the same treatment, may exhibit 
widely varying degrees of chromatin precipitation. 
A consideration of the above mentioned facts may perhaps lead to 
a possible reconciliation of the divergent views expressed by those who 
have studied the supposed relation of prochroniosomes to the genesis of 
the chromosomes themselves. 
General considerations. 
It is now proposed to discuss 1. the significance of the chromatic 
bodies in resting nuclei, and 2. the evolution of the heterotype chromo- 
somes. 
I. Significance of the chromatic bodies. 
It is a widely held view that chromosomes have a permanent individ- 
iiality which is maintained throughout successive generations of cell 
division. One of its chief opponents is Fick (Iß), who regards the chromo- 
somes as tactical entities which appear at the time of nnclear division 
and act as “mobile Manöverirverbände des Chromatins” (p. 202). Stras- 
BURGER (54 and 55) has discussed at length two facts which strongly 
Support the theory of the permanence of chromosomes; firstly, theü' ap- 
pearance in each successive nnclear division, not only in specific numbers, 
but also in characteristic shapes and sizes ; and secondly, the pairing of 
homologous chromosomes in somatic niitoses. These are familiär facts 
and need no further comment. Moreover Strasburger (55) believea 
