12 The Gemmule vs. the Plastidule as the [January, 
THE GEMMULE VS. THE PLASTIDULE AS THE ULIH 
MATE PHYSICAL UNIT OF LIVING MATTER. 
BY JOHN A. RYDER. 
S is well known to every well informed person, protoplasm is 
now regarded as the substance which enters universally and 
constantly into the composition of the living form-elements or 
cells of all living things. It is, therefore, the material basis of 
life. All the varieties of organic structure, no matter how differ- 
ent from each other, have been primarily differentiated from 
apparently homogeneous protoplasm. Premising, therefore, that 
we understand that all histological differences presented by the 
tissues of living organisms arise by differentiations of, or secre- 
tions, derivatives of p/astids (cells) primitively alike, we are ready 
to consider the theories advanced to account for the phenomenon 
of hereditary transmission. Transmission or heredity may be 
defined as that inherent tendency acquired from ancestry and 
manifested by developing or growing organisms to become essen- 
tially like, in appearance and structure, their immediate ancestor 
or ancestors, if the parentage be a sexual one. The appearance 
of a characteristic belonging to a remote ancestor in a new organ- 
ism, which characteristic did not belong to its immediate ancestor, 
is said to be a case of reversion or atavism. This is explained 
upon the assumption—a rational one—that in the germinal matter, 
that is, a plastid, or an egg-cell or a sperm-cell or cells, if reproduc- 
tion be sexual, derived from the immediate ancestor, may still 
inhere a tendency to develop characteristics belonging to the 
most remote of, an indefinite number of removes back, from such 
immediate ancestor. The tendency to develop such palzonto- 
logical characters is supposed to remain in a latent or potential 
state in all those generations intermediate between the ancestor 
in which this characteristic was present and the young organism 
in which it has again made its appearance. In this way gradually 
but continuously, and adaptively acquired characteristics are trans- 
mitted, as well as habits. It may be that profound and enduring 
sensory impressions upon the maternal organism in higher forms, 
by their persistence, may produce immediate effects upon the 
offspring which cannot be attributed to ancestry. The many 
a et Section of the Academy of Natural Sciences, of Philadelphia. 
i 
ae the substance of an essay read before the Microscopical- and Biologi- 
