PARASITISM AND SYMBIOSIS — CAULLERY. 409 



effort which has been put forth since 1859 under the impulse of 

 Darwin's book has not led us to the essential solution of the problem 

 of transf ormism ; it may even leave certain persons at the present 

 moment in a rather discouraged state of mind. But this effort has 

 brought us to an incomparably more advanced knowledge of animal 

 forms, of their intimate structure and of the manner in which they 

 are developed. It is thanks to this progress that we see the im- 

 possibility of certain explanations which seemed almost obvious im- 

 mediately after 1859. And the very difficulties presented by the 

 problem of adaptation make it inevitable that morphology can not 

 reduce itself to a few simple laws. It is, moreover, through the 

 progress which has been accomplished that we have been able to 

 state, and shall be able to state, in the physiological field, the ques- 

 tions which appear to use to be the most interesting. What would 

 all the experiments on the animal e,gg amount to if we were ignorant 

 of all that morphological embryology has taught us? Morphology 

 still offers an endless field for learning, and the facts yet to be dis- 

 covered may be decisive in directing physiological research. For my 

 part, therefore, I hold that it is not correct to say that the interest in 

 morphology is exhausted and that we ought to turn away from it or 

 turn younger investigators away from it. Should morphology be 

 too much neglected the foundation on which modern cellular phys- 

 iology would rest would rapidly become insufficient. We can not do 

 otherwise than deeply admire, even to-day, that which Claude Ber- 

 nard wrote in his " Lecons sur les phenomenes de la vie communs aux 

 animaux et aux vegetaux" about the individual characters and the 

 respective parts of morphology and physiology. And yet when we 

 see, a little further along in the volume, what he was able to say, at 

 his time, about the general phenomena of the development of the egg 

 we can measure how vast and fertile a field the work of the mor- 

 phologist has since then furnished for the physiologist. This fer- 

 tility of morphology is not exhausted. The study of parasitism 

 which we are going to take up will confirm our opinion that mor- 

 phology and zoology are not ended and that it is worth while to con- 

 tinue to work on them, without for that reason failing to recognize 

 the enormous interest offered by the physiological method. And 

 what good can come from setting in opposition two methods which 

 ought to support each other mutually, and each of which is better 

 fitted to the peculiarities of certain minds? 



