Evidence from Protorsoaris ,'J9.*J 



while the chromosomes disintegrate into ^raniiKs, which 

 again form the large chromatin reservoirs, characteristic 

 of Noctiluca.^* ^- 



The matters of cliief interest for us in this account an- 

 the extra-nuclear position of the division center; its hum' 

 size, making the observation of it ahnost as practicable us 

 observation of the nucleus itself; the sliarj) distinction, in- 

 dicated by the difference in staining, between tlie mateii.il of 

 the division center and the nuclear contents, j)art icularl v 

 the chromatic part of tlie contents; the unmistakablv in 

 dependent and leading ])art ])laye(l by the center in division, 

 the split chromosomes, for example, being separated 

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

 part of the sphere; and finally the strong direct evidence 

 that the activities of the center jjcrtain to the substance of 

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

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

 point it should be said that Calkins found considerable evi- 

 dence that the centrioles (centrosomes accordiiig to tlie 

 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 ami 

 only migrate into the center during the divisional activity 

 of the center and the nucleus. But granting to this miiuiti- 

 granule all that actual observation entitles it to, tlu most 

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

 complex series of changes and transformaticjiis which con- 

 stitute the propagation-division of the animal. Calkiro' 

 statement that "A cytoplasmic sul)stance, corresponding to 

 the centrosphere of many metazoan cells, is invariably j)res- 

 ent. It is a permanent organ of the cdl, often as largi-, or 

 larger, than the nucleus; it divides to form an aM!|>hiii.ster, 

 consisting of two asters with coiuiecting ma nth fibres, the 

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

 I mean by this is that we have no right to j)in our faith to 



