Evidence from Prntozoavs 363 



If WG liold firmly to this broad but, in the light of facts, 

 only adequate conception of heredity, the general answer to 

 the questions stated above as to the relation of chromosomes 

 to heredity will come without equivocation. We may give 

 the answers now categorically, then look at the facts which 

 compel them. Neither chromosomes nor chromatin are the 

 sole bearers of heredity. Factors for hereditary attributes, 

 if the teiTn has any real meaning as thus used, are "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 heredity. 



Evidence From the Ontogeny of Variotis Protozoans 



Beginning the discussion again with the lower organisms 

 and advancing to the higher, we first examine the develop- 

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

 what follows in connection with the chapters on the struc- 

 ture, and especially on the development of protozoans. 



(a) Stentor 



The development of the "trumpet animalcule," Stentor, 

 having been instanced as a genuine, often complex ontogeny 

 in protozoans, our study of heredity in the protozoa may 

 well begin with this animal. The figures 11, 12, 13, and 14 

 accompanying the earlier presentation will serve us now. 

 Reference to the account given in the 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 part of the endoplasm. "And 

 this de novo mode of origin," we read, "is followed by a 

 whole series of organs and tissues ; the cilia and membranel- 

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

 frontal field; the ramifying zone; and the contractile vacu- 



