C. DOBELL 143 



which the weakened descendant may be restored to new vigor is 

 by conjugation with another individual" (Calkins and Lieb, 1902). 

 "A couple of hundred generations, more or less, uses up the potential 

 of vitality, whereupon, unless the potential is renewed [by conjugation 

 or stimulation], the race dies out with some indications of protoplasmic 

 old age" (Calkins and Lieb, 1902). 



29. Calkins (1904) denied that the meganucleus increases in size 

 during depression periods, or that the micronucleus degenerates (contra 

 Maupas). " Temperature changes have little or nothing to do with the 

 decline of vigor" (Calkins, 1902). Depression is not morphological, but 

 physiological, and is shown by pathological divisions and the formation 

 of monsters, decrease in the rate of division, and death. The recovery 

 from depression — brought about by chemical stimuli — he regarded as 

 a case of " artificial parthenogenesis." This is based, apparently, upon 

 the erroneous supposition (§§ 12, 14) that the conjugant — or would-be 

 conjugant — is a gamete. 



30. R. Hertwig has formulated a hypothesis to account for the 

 "depression" periods observed by himself, Calkins, and many others, 

 in cultures of ciliates. It is involved in his " theory of the karyoplasmic 

 ratio " (Kernplasmatheorie) which may be stated as follows : the mass- 

 relation of nucleus to cytoplasm expressed as the quotient ^ — that is, 



the mass of nuclear substance divided by the mass of cytoplasm — is 

 a ratio whose magnitude is of fundamental importance for all vital 

 processes influenced by the nucleus, for assimilation and organizing 

 activity, for growth and division (R. Hertwig, 1908, p. 5, et alibi — 

 cf. 1899, 1902, 1903, 1903 a, 1905). 



31. Hertwig (1899, 1903, 1903 a), from studies of Paramecium, 

 Dileptus, and other Protozoa, believes that depression is due to the 

 development of an abnormal karyoplasmic ratio. During a number 

 of successive generations, the nucleus gradually increases in size at the 



expense of the cytoplasm — in other words, ^ becomes larger. The 



resulting disproportion causes depression, or inhibition of vital activities. 

 It may be compensated by elimination or absorption of nuclear substance, 

 or by conjugation — both of which are considered to restore the karyo- 

 plasmic ratio to normal : or it may be so great a disproportion that the 

 animal is unable to recover, and consequently dies. Hertwig found 

 that the meganucleus actually is disproportionately large in animals 

 in a state of depression. 



10—2 



