558 The American Naturalist. [July, 
and every individual who succumbs to this disease can reflect 
with melancholy satisfation that he does so pro bono publico. 
Conclusions as to the Factors of Evolution —The conclusions 
we reach from the study of the muscular and skeletal systems 
are therefore as follows: 1st. That individual transformism in 
the body is the main determinant of variations in the germ- 
cells, and is therefore the main cause of definite progressive or 
retrogressive variations in single organs. 2d. That evolution 
in these organs is hastened, where all members of the race are 
subject to the same individual transformism. The contrast 
between the rate of individual transformism and race trans- 
formism is due to the strong conservative forces of the germ- 
plasma. 3d. That evolution is most rapid where variations 
are of sufficient rank to become factors in survival. Then 
selection and use-inheritance unite forces, as active progressive 
principles opposing the conservative principle in the germ- 
plasma. 4th. That fortuitous and chance variations also 
arise from disturbances in the body or germ-cells; they may 
be perpetuated, or disappear in succeeding generations. 
Applying these views to variation there should, theoretically, 
appear to be just those two distinct classes of anomalies in the 
human body which we have seen actually occurring. First, 
those in the path of evolution, arising from perfectly normal 
changes in the somatoplasm and germ-plasm. Second, those 
wholly unconnected with the course of evolution, arising 
fortuitously or from abnormal changes in the somatoplasm or 
erm-plasm ; to this head may be attributed the whole scale 
of deformities. Thus transformism and de-formism should be 
kept distinct in our minds. Nevertheless the facts of de-form- 
ism contribute the strongest body of evidence which we can 
muster at present to prove that there does exist a relation 
between the somatoplasm and germ-plasm which renders 
transformism possible. 
* 
The Relations between the Somatoplasm and Germ- 
plasm.—We have seen reasons to take a middle ground as to 
the distinct specific nature of the body cells and germ cells, 
and this position is, I think, strengthened the more broadly 
