40 GENERAL SKETCH OF THE CELL 



reasons most observers (Biitschli, Gruber, Schewiakoff, Nadson, etc.) 

 regard them as true chromatin-granules which represent a scattered or 

 distributed nucleus not differentiated as a definite morphological body. 

 If this identification is correct, such forms probably give us the most 

 primitive condition of the nuclear substance, which only in higher 

 forms is collected into a distinct mass enclosed by a membrane ; and 

 the scattered granules are comparable to those forming the chro- 

 matin-reticulum and chromosomes in the higher types. The identi- 

 fication is, however, difficult, owing to the impossibility of actual 

 chemical analysis ; and Fischer ('97) has shown in the case of the 

 Bacteria and Cyanophyceae that we cannot safely trust either the 

 staining reactions or the digestion test, since the former are variable, 

 while the latter does not differentiate the granules from some other 

 cytoplasmic constituents. 1 It is, however, certain that the staining 

 power of chromatin in the higher forms varies with different condi- 

 tions, and furthermore there is reason to believe that these granules 

 may divide by fission. Besides these observations of Schewiakoff on 

 Achromatium (see above), we have those of several authors on 

 Infusoria, and more recently those of Calkins on flagellates, 

 both pointing to the same conclusion. Balbiani, Gruber, Maupas, 

 and others have described various Infusoria (Urostyla, Trachelocerca, 

 Holosticha, Uroleptus\ as well as some rhizopods {Pelomyxa\ in 

 which the body contains very numerous minute chromatin-granules 

 of "nuclei" (Fig. 15), which Gruber ('87) showed to multiply by 

 division. Balbiani ('61) long since showed that in Urostyla these 

 bodies become concentrated toward the centre of the ceil at the time 

 of division, and Bergh ('89) demonstrated that they then fuse to form 

 a macronucleus of the usual type, that elongates, assumes a fibrillar 

 structure, and divides by fission. After division of the cell-body 

 the macronucleus again fragments into minute scattered granules, 

 which in this case certainly represent a distributed nucleus. In the 

 flagellate Tetramitus Calkins ('98, i) likewise finds numerous scat- 

 tered chromatin-granules, which at the time of division become aggre- 

 gated into a single dividing mass (p. 92); while in other forms the 

 mass (nucleus) persists as such without (Trachelomonas, Lagenella, 

 Chilomonas) or with (Euglena> Synura) a surrounding membrane. 



Taken together, the foregoing facts, while certainly not conclusive, 

 give good ground for the provisional acceptance of Biitschli's con- 

 ception of the distributed nucleus, and indicate that nucleus and 

 cytoplasm have arisen through the differentiation of a common 

 protoplasmic mass. The nucleus, as Carnoy has well said, 2 is like a 



1 It should be remembered that we have no unerring " chromatin-stain." Cf. p. 335. 

 2 '84, p. 251. 



