206 PREFACE. 



merit of the mesoblast, and must be regarded as affording a 

 conclusive demonstration, that in the case of Vertebrata the 

 mesoblast has primitively the form of a pair of diverticula from 

 the walls of the archenteron. 



The present Memoir, while differing essentially in scope and 

 object from the two important treatises by Professors His 1 and 

 Gotte 2 , which have recently appeared in Germany, has this 

 much in common with them, that it deals monographically with 

 the development of a single type : but here the resemblance 

 ends. Both of these authors seek to establish, by a careful 

 investigation of the development of a single species, the general 

 plan of development of Vertebrates in general, if not of the 

 whole animal kingdom. Both reject the theory of descent, as 

 propounded by Mr Darwin, and offer completely fresh explana- 

 tions of the phenomena of Embryology. Accepting, as I do, 

 the principle of natural selection, I have had before me, in 

 writing the Monograph, no such ambitious aim as the establish- 

 ment of a completely new system of Morphology. My object 

 will have been fully attained if I have succeeded in adding a 

 few stones to the edifice, the foundations of which were laid by 

 Mr Darwin in his work on the Origin of Species. 



I may perhaps call attention to one or two special points in 

 this work which seem to give promise of further results. The 

 chapter on the Development of the Spinal and Cranial Nerves 

 contains a modification of the previously accepted views on this 

 subject, which may perhaps lead to a more satisfactory con- 

 ception of the origin of nerves than has before been possible, 

 and a more accurate account of the origin of the muscle-plates 

 and vertebral column. The attempt to employ the embryo- 

 logical relations of the cephalic prolongations of the body-cavity, 

 and of the cranial nerves, in the solution of the difficult problems 

 of the Morphology of the head, may prove of use in the line of 

 study so successfully cultivated by our great English Anatomist, 

 Professor Huxley. Lastly, I venture to hope that my con- 

 clusions in reference to the relations of the sympathetic system 

 and the suprarenal body, and to the development of the meso- 



1 Erste A nlage des IVirbelthierleibes. 

 - Entwickltingsgesehichte dcr Unkc. 



