THE EVOLUTION OF PROTOZOA. 311 



well-provided types, whether among the other Hijpotricha or in 

 any other group. 



Examples might be multiplied almost indefinitely, did space 

 permit. But perhaps sufticient has been said to form an outline 

 of the question under discussion — an outline admittedly sketchy 

 and suffering from over-compression. The gaps necessarily left 

 in the arguments and examples many readers will be able to fill 

 in for themselves. 



Although this paper is of intention critical, yet it would be 

 hardly fair not to give some idea of what forces may have been 

 at work to produce the results described. 



A factor which suggests itself at once is that of the inherit- 

 ance of characters acquired by use. Thus the development of 

 spines in Ilaltcria might be explained as due to the exercise of 

 rudimentary spines producing their greater development in the 

 individual, and as a result a modification of the germ-plasm in 

 the same direction. But since experiment has shown, I believe 

 conclusively, that somatic modifications are not transmissible 

 even in unicellular forms, this hypothesis breaks down ; though 

 Lloyd Morgan's theory, that acquired characters may favour the 

 propagation of mutations in the same direction, is important in 

 this connection. 



Probably the best explanation is to be found in some form 

 of the orthogenesis theory, of continual progress in a straight 

 line. A germinal mutation caused by change in the environment 

 (in the broad sense of the term) produces change in the cytoplasm, 

 and this change forms a kind of groove along which more muta- 

 tions in the same direction accumulate. 



To many a physico-chemical statement of such a process 

 would be all-sufficient ; but to others, myself among the number,, 

 such a statement seems only to give us an idea of the steps of 

 the process, not one of the process as a whole. The problem of 

 organic evolution lies deeper still. How can a mechanical 

 statement of the orthogenesis theory explain, say, the marvellous- 

 correlation of variation manifested in the evolution of the 

 vertebrate eye ? As I say, the riddle's solution lies deeper. 

 Each step in variation is physico-chemical, but variation 

 itself is essentially the expression of the free creativeness of 

 Life, of that "new form of energy" which inhabits protoplasm. 



