1888 - 89 .] Mr J. A. Thomson on Theory of Heredity. 105 
tions of His, Rauber, and others, there are few general facts on 
which one can find foothold for further construction. Yet the 
task has been more than begun in the experimental investigations of 
O. Hertwig, Fol, Pfliiger, Born, Roux, Schultze, Gerlach, and others. 
Observations as to the actual dynamics of cell division — such, 
for instance, as those of Van Beneden and Boveri, — are beginning 
to appear; while the title of Berthold’s book on “Protoplasmic 
Mechanics” shows how the biologist begins to seek the aid of 
the student of physics in explaining the architecture of the living 
organism. But we are at present only concerned in emphasising 
that the conception of development as what Pfliiger called “ organic 
crystallisation ” must become dominant. The laws of growth which 
express the mode in which each fertilised egg-cell must undergo 
segmentation, gastrulation, and the like have to be expressed in 
terms of the internal and external physico-chemical conditions . 
“To think that heredity will build organic beings without 
mechanical means is a piece of unscientific mysticism,” as Professor 
His noted in his valuable paper recently submitted to this Society, 
and yet the tendency does not rapidly disappear from even scientific 
literature. It is impossible, for instance, to exaggerate the import- 
ance of the general conclusion variously expressed by Yon Baer, 
Spencer, and Haeckel, that the life-history of the individual is a 
recapitulation of the evolution of the race. To say that ontogeny 
recapitulates phylogeny, or that “ the microcosm of the ontogenetic 
tree is a reflection of the macrocosm of the genealogical tree,” is to 
express a marvellous generalisation. But what we now wish to 
understand is, as Hallez expresses it, how the protoplasm is at each 
stage the architect as well as the material of its own development. 
The metaphors suggest that the developing organism has somehow 
a feeling for history, or that the dead hand of the past is literally 
upon the present, while our aim must be to get beyond any mere 
phrase of organic memory, and to understand the chemical and 
physical conditions which, more or less modified in the course of 
history, must still be present to rule the development. There can 
be no doubt that, in the modern theory of continuity, there is found 
the reconciliation between those who maintain that the likeness of 
offspring to parent is due to the presence of similar conditions and 
those who are satisfied in referring the resemblance simply to 
