EMBRYOLOGICAL SYSTEMS. 359 



evident from this that he has clearly perceived the limita- 

 tion of the different modes of embryonic development 

 within the respective branches of the animal kingdom; 

 but it is equally certain that Ins assertions are too general 

 to furnish a key for the comparison of the successive 

 changes which the different types undergo within their 

 respective limits, and that he is still vaguely under the 

 impression that the development corresponds, in its indi- 

 vidualization, to the degrees of complication of structure. 

 This could hardly be otherwise as long as the different 

 categories of the structure of animals had not been clearly 

 distinguished. 1 



CLASSIFICATION OF K. E. VON BAER. 



In conformity with his embryological investigations, K. E. von Baer pro- 

 poses the following classification : 



I. Peripherie Type. (RADIATA.) Evolutio radiata. The development 

 proceeds from a centre, producing identical parts in a radiating 

 order. 



II. Massive Type. (MOLLUSCA.) Evolutio contorta. The development 

 produces identical parts curved around a conical or other space. 



III. Longitudinal Type. (ARTICULATA.) Evolutio gemina. The develop- 

 ment produces identical parts arising on both sides of an axis, 

 and closing up along a line opposite the axis. 



and four modes of development. He trary, Cuvier's special object for 



only adds : " It is barely possible, many years was to point out these 



that, in their first beginning, all aui- plans, and to show that they are 



mals are alike." Huxley must also characterized by peculiar struc- 



have overlooked Cuvier's introduc- tures ; while Baer's merit consists in 



tion to the " Regne Animal" (2nd having discovered four modes of de- 



edit., vol. 1, p. 48, quoted verbatim velopment, which coincide with the 



above, p. 309), when he stated that branches of the animal kingdom, in 



Cuvier " did not attempt to discover which Cuvier recognized four differ- 



upon what plans animals are con- ent plans of structure. Huxley is 



structed, but to ascertain in what equally mistaken when he says that 



manner the facts of animal organiza- Cuvier adopted the nervous system 



tions could be thrown into the fewest " as the base of his great divisions." 



possible propositions." On the con- 1 Compare Chap. II, Sect. 1 to 9. 



