1888 .] Prof. Wilhelm His on Animal Morphology. 
295 
deny the immense progress that biological science has made, by 
introducing this grand conception into the horizon. Questions of 
phylogeny will be for long of the utmost importance, and of the 
greatest interest in biology ; but the single word “ heredity ” can- 
not dispense science from the duty of making every possible inquiry 
into the mechanism of organic growth and of organic formation. 
To think that heredity will build organic beings without mechanical 
means is a piece of unscientific mysticism. 
Heredity is the general expression of the periodicity of organic 
life. All generations belong to a continuous succession of waves, 
in which every single one resembles its predecessors and its fol- 
lowers. Science has to analyse the periodic process of life in the 
individual phenomena as well as in the totality, the precise notions 
of the former being the base of the more embracing conceptions. 
By comparison of different organisms, and by finding their simi- 
larities, we throw light upon their probable genealogical relations, 
but we give no direct explanation of their growth and formation. 
A direct explanation can only come from the immediate study of 
the different phases of individual development. Every stage of 
development must be looked at as the physiological consequence of 
some preceding stage, and ultimately as the consequence of the acts 
of impregnation and segmentation of the egg. 
Some of the modern publications may be considered as symptoms 
that embryological studies are about to take a more physiological 
direction. The important inquiries of O. Her twig, Fol, Pfliiger, 
Born, Roux, Gerlach, and others, regarding impregnation, the first 
axes of segmentation, and the artificial formation of deformities, are 
based upon physiological ideas and physiological methods, and they 
open new and large fields for biological investigation. 
Physiological considerations in morphology are far from inter- 
fering with phylogenetic inquiries ; rather will the phylogenetic 
worker find in them a mighty help in his efforts. He has only to 
open his eyes to the actual processes of life and development. The 
operations which nature performs under our eyes cannot be different 
in principle from her processes in remote periods ; and a good notion 
of the actual natural processes may, even for phylogenetic purposes, 
be much more useful than rigid morphological diagrams, abstracted 
by merely logical operations. 
