52 
SPERMATOGENESIS OP NORMAE 
Ewart^, in a recent paper, gives some beautiful corroborative 
evidence. 
To explain reversions, some investigators presuppose the 
existence of latent elements which have lain dormant for per¬ 
haps many generations and which in some unknown manner 
later reassert themselves. Others, on the contrary, maintain 
that the resemblance is produced through a recurrence of suit¬ 
able external conditions, such as existed during the ancestral 
period. A third and apparently simpler possibility arises if w’e 
conceive of the cytoplasm as the more conservative, or stable, 
and the chromatin, the more individual and variable agent in 
the germ cell. Thus, if little chromatin were present, or if it 
were inactive for any reason, as, for instance, if certain qual¬ 
ities neutralized each other, then from the cytoplasmic portion 
would develop the general or ancestral type which is the same 
for all the kindred forms. The cumulative individual charac¬ 
ters latest added to the chromatin would remain in abeyance 
and the result would be what is called reversion. No latent 
germs are necessary beyond the original fundamental ground 
substance of the type, for the reversion is not due to a reas¬ 
sertion of a latent germ, but to the suppression of the later 
developed characters which are transmitted through the chrom¬ 
atin. 
After having penned the above the writer was very much 
interested in noting that Bwart^ voices much the same idea 
regarding reversion although he suggests no localization in the 
germ-plasm. Speaking of reversions in pigeons, he remarks: 
“Perhaps I may here say that reversion is more a negative than 
a positive influence, that if I understand it aright complete re¬ 
version is mainly due to the development being abruptly 
arrested so as to reproduce a lost ancestor. Sometimes several 
printings are required to produce a coloured plate. Were one 
or more of the printings omitted a kind of 'reversion’ would be 
the result. When the owl and archangel are crossed the latest 
colours added by the fancier are not reproduced, and the older 
and simpler colours are again made visible. When the white 
fantail and owl-archangel were crossed all the recently acquired 
1. Ewart, J. C: The Penycuik Experiments., 1899. 
2. Ewart, J. C: The Penycuik Experiments., 1899, page xxviii. 
