Evidence from Protozoans fUJ'i 



If we hold firmly to this l)roa(l hut, in tin- h^rlit of facts, 

 only adequate eonce])tion of lierechty, the general answer to 

 the questions stated ahove as to tlie relation of clironiosomes 

 to heredity will come without e(jui\ ocat ion. \\\ niav i;ive 

 the answers now categorically, then look at the facts which 

 compel them. Neither chromosomes nor chromatin arc the 

 sole bearers of heredity. Factors for hereditary attributes, 

 if the term has any real meaning as thus used, arc "carried" 

 by the cytoplasm no less than by the chromatin. .Many, 

 probably all living parts of the cell, and not the chromatin 

 and chromosomes alone, are the physical bases of hereditv. 



Evidence From the Ontocjeny of Various Protozoans 



Beginning the discussion again with the lower organisms 

 and advancmg to the higher, we first examine the develojy- 

 ment of a few protozoans; and the reader is urged to take 

 wdiat follows in connection with the chapters on the struc- 

 ture, and especially on the development of protozoans. 



(«) Stentor 



The development of the "trum})et animalcule," Stentor, 

 having been instanced as a genuine, often com])le\ ontogeny 

 in protozoans, our study of heredity in the protozoa may 

 well begin with this animal. The figures 11, 1!^, Il5, and 14 

 accompanying the earlier presentation will serve us now. 

 Reference to the account given in tiie former discussion finds 

 that one of the main points brought out was that in repro- 

 duction a whole series of the Stentor s external organs arise 

 de novo, that is, independently of the corresponding organs 

 of the parent; and that these take their origin in the surface 

 layer or ectoplasm, and outer })art of the endo|)lasm. "And 

 this de novo mode of origin," we read, ''is followi-d by a 

 wdiole series of organs and tissues: the cilia and iniini)i-anil- 

 lae of the aboral zone; the mouth, velum and pharynx: the 

 frontal field; the ramifving zone; and the coid ractile vacu 



