122 STUDIES IN ANIMAL LIFE. 



Although I conceive the doctrine of fixity of 

 species to be altogether wrong, I can not say that 

 the arguments adduced in favor of the development 

 hypothesis rise higher than a high degree of proba- 

 bility, still very far from demonstration ; they will 

 leave even the most willing disciple beset with dif- 

 ficulties and doubts. When stated in general terms, 

 that hypothesis has a fascinating symmetry and 

 simplicity ; but no sooner do we apply it to partic- 

 ular cases, than a thick veil of mystery descends, 

 and our pathway becomes a mere blind groping to- 

 ward the light. There is nothing but what is per- 

 fectly conceivable, and in harmony with all analo- 

 gies, in the idea of all animal forms having arisen 

 from successive modifications of one original form, 

 but there are many things perfectly conceivable 

 which have nevertheless no existence ; there are 

 many explanations perfectly probable which are 

 not true ; and when we come to seek for the evi- 

 dence of the development hypothesis, that evidence 

 fails us. It may be true, but we can not say that it 

 is true. Ten years ago I espoused the hypothesis, 

 and believed that it must be the truth; but ten 

 years of study, instead of deepening, have loosened 

 that conviction : they have strengthened my oppo- 

 sition to the hypothesis of fixity of species, but 

 they have given greater force to the difficulties 

 which beset the development hypothesis, and have 

 made me feel that at present the requisite evidence 

 is wanting. I conclude with reminding the reader 



