310 Hubert P. Yockey 



a series of generations each produced from eggs laid on a given day in the 

 life of the parent. Lansing called such a series an 'orthoclone'. An orthoclone 

 obtained from a senile stage in the life of the rotifer was designated as an old 

 orthoclone or a 'geriaclone' whereas an orthoclone from adolescent organisms 

 was called a young orthoclone or a 'pediaclone'. 



For each species it was found that the geriaclone could be followed to 

 extinction in a few generations. In the case of Philodina citrina even the six-day 

 orthoclone died out in the seventeenth generation. It was observed that the 

 longevity of the five-day orthoclone tends to increase. The maximum life span 

 of that orthoclone was not found but appeared to be indefinite. 



It was found for each species of rotifer that the life shortening could be 

 reversed by starting a pediaclone as an off shoot from a geriaclone. The limit 

 to the ability to lengthen life seemed to be the fact that egg production does 

 not appear until about the fifth day for Philodina citrina and about the fourth 

 day for Euchlanis triquetra. 



The number of animals used to establish a life table was sixty, a number too 

 small to avoid considerable fluctuations. However, the curves shown in 

 Lansing's papers give the impression that the shape of the survival curves is 

 maintained. This feature seems to be in common with data discussed above 

 in Section III, and in particular with the work of Furth et al. (48), on the late 

 effects of ionizing radiation on mice. 



The decline and extinction of viability in the germ line is accounted for 

 in the present theory by the accumulation of equivocation in the gene code 

 as it is transmitted in the germ line. The recovery is regarded as being due 

 to selection and propagation of that portion of the ensemble with a relatively 

 low amount of equivocation. 



The explanation offered by Lansing is quite different from that given here. 

 He attributes his results to a transmissible factor which appears at cessation 

 of growth. In particular, his assertion that the factor is non-genic appears 

 to contradict the point of view adopted here. Actually there is no contradiction 

 with the latter assertion since Lansing v/as undoubtedly thinking of genetic 

 factors in terms of the ideas concerning the gene current at the time of writing, 

 and indeed today. However, as Lansing notes, 'it is striking that the experi- 

 mental observations on the primitive rotifer as well as conclusions derived 

 therefrom are entirely compatible with conclusions drawn from mammalian 

 experiments.' The feature of these and other organisms which is the same 

 is the chemical composition of the genetic material and for this and other 

 reasons it seems to me that an explanation for so ubiquitous a phenomenon 

 as aging must be related to the genome. 



The germ line provides an opportunity to study the error correction function 

 of conjugation. The most extensive data relating damage in the germ line 

 from one parent or both to survival seem to be due to Mortimer (31, 61). 

 He obtained survivorship curves for yeast zygotes formed by the conjugation 

 of cells of opposite mating types. The following crosses were obtained: haploid 

 X haploid (oo), haploid X diploid (oO), diploid X haploid (Oo), and diploid 

 X diploid (OO). In the symbolism used a capital O represents a diploid cell, 

 a lower case o represents a haploid cell; a filled letter (#0) irradiation. The 

 first symbol indicates the a-mating, the second the a-mating type. 



