225 
it or eise lack it. Tkis is the very limit of simplicity, and it 
requires no special study to see that there is no corresponding 
simplicity in the relation between a parent's final qualities and 
tliose of its offspring. William Ritter has emphasized the impor- 
tance of studying tliings as they are in biology, and not as they 
miglit be^ or ought to be on some or other theory. I fully agree 
with this view^ biit I think we need never give up trying to 
analyze complex processes like development into the different 
fundamental factors which give this whole^ simply besause neither 
of these composing single things is by itself able to force its 
simplicity upon the final result. 
In the study of development and evolution^ Mendelism now 
takes a definite and extremely usefull place. 
Systematicians can be said to study the difi*erences and 
analogies between groups of organisms^ each group homogeneous 
for at least a great number of genetic factors, the Biometricians 
are by Statistical methods studying the average effects of Variation 
of both genetic and non-genetic factors in their combined result 
on the Variation of the individuals within these groups. 
The biomechanists concern themselves with the interrelation 
and Cooperation of genetic and non-genetic factors in the deve- 
lopment of the organisms; experimental zoology and botany on 
one band, and Mendelism on the other^ may be conceived as 
two special divisions of the study of biomechanism, experimental 
zoology and botany being chiefly study of the non-genetic factors 
in the development, and of environment on function, Mendelism 
being germinal analysis, the study of the genetic factors in the 
development of the organisms. 
This we must always bear in mind, that Ave are studying 
the genetic factors, their effect upon development, their nature, 
the way in which they are transmitted, the possibility of their 
being influenced, their relations toward one another, and that as 
yet in this study we have not laid our band on any of these 
things, so that we must contend ourselves to notice the diöerence 
it makes to a developing germ whether any one of them is prcsent 
or not. Thus, what we are actually regarding are differences 
between individuals, and we are trying to find out, by carefully 
planned breeding-experiments in how far tliese difi'erences are 
due to the presence or absence of each genetic factor. We have 
abundant evidence that these genetic factors only act hy iiifiuen- 
Verhiindlungen des naturf. Veroinet; in Brünn. XLIX, Band. 15 
