GENETICS: THE HERITABLE TRANSMISSION OF CATALYSTS 173 



out that these two cellular divisions "are not separate in fact and in 

 substance, though they are often kept isolated in concept — to the 

 great detriment of sound understanding. There is a continual cycle 

 of interchange between them, a transformation of material from one 

 into the other . . . The cytoplasm is not merely passive; it actively deter- 

 mines what shall happen in the chromosomes . . . Every cell retains 

 all the chromosomal materials, but which of these materials comes into 

 action in each cell depends upon what cytoplasm is there present, as 

 well as upon the conditions under which the reactions occur . . ." 



In the case of the killifish (Fundalus), A. Richards 17 observed that 

 the condensed chromosomes become vesicular by taking in cytoplasmic 

 material and forming a vesicle hundreds of times the size of the orig- 

 inal chromosome. These swollen chromosomes touch, press together, 

 and form the nucleus. Then the vesicles discharge their content into 

 the cytoplasm, including great numbers of chromatin particles detect- 

 able by cytological methods. The condensed chromosomes for the 

 next cell division are formed from minute reserve parts of the large 

 vesicles. Jennings states: "The pictures that we see of the condensed 

 stages of chromosomes, at the time when they are undergoing division, 

 are most misleading if they are assumed to show the distinctive char- 

 acteristics of chromosomes. The chromosomes are active and change- 

 able; they continually operate on the remainder of the cell (which we 

 lump together as cytoplasm), visibly interchanging material with the 

 cytoplasm, altering it, differentiating it . . ." Professor E. G. Conklin 18 

 summarized his similar observations on the common slipper-limpet 

 Crepidula thus: "One might speak of these changes in the nucleus as 

 systole and diastole, by means of which an exchange of nuclear and 

 cytoplasmic material is brought about." But it must be remembered 

 that the material discharged by the vesicles has been subjected to the 

 influence of the local catalysts, including the genes and the enzymes 

 arising from them. 



Jennings then lists three classes of heritable modifications in pro- 

 tozoa: (1) degenerate changes induced by unfavorable conditions 

 acting for many generations; (2) acclimatization to high or low tem- 

 peratures or to injurious concentrations of chemicals (As, Sb, quinine, 

 methylene blue and various organic substances); and (3) alterations in 

 form and structure not involved in (1) and (2), which may be re- 

 tained for hundreds of generations. Referring to the work of G. F. 

 De Garis 19 on Paramecium caudata through a long series of asexual 

 generations, Jennings remarks: "At every succeeding fission the orig- 

 inal cytoplasm is diluted to one-half, so that after ten generations it is 

 diluted to less than 1/1000 part, the remainder being new cytoplasm 

 produced by growth. Yet after ten generations the original cytoplasm 

 still has a marked effect on size. The original cytoplasm seemingly 

 must therefore have to some extent the power of reproducing itself 



