Evidence from Protozoans B93 



while the chromosomes disintegrate into granules, which 

 again form the large chromatin reservoirs, characteristic 

 of Noctiluca.'' ^^ 



The matters of chief interest for us in this account are 

 the extra-nuclear position of the division center; its large 

 size, making the observation of it almost as practicable as 

 observation of the nucleus itself ; the sharp distinction, in- 

 dicated by the difference in staining, between the material of 

 the division center and tlie nuclear contents, particularly 

 the chromatic part of the contents ; the unmistakably in- 

 dependent and leading part played by the center in division, 

 the split chromosomes, for example, being separated 

 "through the agency of the mantle-fibres," these latter a 

 part of the sphere ; and finally the strong direct evidence 

 that the activities of the center pertain to the substance of 

 the center itself and are not caused entirely by a "force" or 

 "influence" of the centriole. With reference to the last 

 point it should be said that Calkins found considerable evi- 

 dence that the centrioles (centrosomes according to the 

 nomenclature employed by him) which are easily recogniz- 

 able in the division center during advanced stages of nuclear 

 division, are in the nucleus during the resting period and 

 only migrate into the center during the divisional activity 

 of the center and the nucleus. But granting to this minute 

 granule all that actual observation entitles it to, the most 

 that can be said is, that it is an active participant in the 

 complex series of changes and transformations which con- 

 stitute the propagation-division of the animal. Calkins' 

 statement that "A cytoplasmic substance, corresponding to 

 the centrosphere of many metazoan cells, is invariably pres- 

 ent. It is a permanent organ of the cell, often as large, or 

 larger, than the nucleus ; it divides to form an amphiaster, 

 consisting of two asters with connecting mantle-fibres, the 

 central-spindle," ^^ should be taken at its face value. What 

 I mean by this is that we have no right to pin our faith to 



