APPENDIX D2. 



THE ANNULOSE TYPE. 



THE production of a segmental structure by undulatory move- 

 ments, suggested in Appendix D, as also in B (first published in 

 1858) as explaining the vertebral column, has been recently 

 suggested by Prof. Korschelt as the cause of that segmentation of 

 the annulose type which gives the name to it. He espouses a 



" view which is based upon the assumption that at first an unsegmented, 

 elongated ancestral form was produced by terminal growth, whereupon the 

 entire body became separated at once into a large number of segments by a 

 rearrangement of the individual organs. This assumption is supported by 

 the consideration that with the lateral sinuous movement of the body, and 

 with the rigidity of the tissues caused by increasing differentiation, the 

 formation of alternating regions of greater and less motility was of con- 

 siderable advantage to the individual, and rendered possible a further elon- 

 gation of the body. The first cause for the appearance of metamcric 

 segmentation would then be sought in the manner of locomotion and in 

 mechanical conditions. However, this latter view is not supported in any 

 way by embryology." (Embryology of Invertebrates, Part I, pp. 349-50.) 



I venture to think the confession that this view " is not sup- 

 ported in any way by embryology " should be joined with the 

 confession that it is at variance with that abstract embryology 

 which comprehends the process of development in general. The 

 assumption that there took place "a rearrangement of the 

 individual organs " of " an unsegmented, elongated ancestral 

 form," in such wise that the organs, previously single, presently 

 became multiple, so that instead of one organ of each kind there 

 were substituted many organs of each kind, is inconsistent with 

 the general law of evolution, organic and other implies not 

 integration but disintegration. Everywhere the advance is from 

 many like parts performing like functions to relatively few unlike 

 parts performing unlike functions. The higher forms of the annu- 

 lose type itself show this. Compare a myriapod and a crab. In the 

 one we have not only a great number of similar segments bearing 

 similar limbs, but we have in each segment a dilatation of the main 

 blood-vessel a rudimentary heart a swollen portion of the 

 nerve cord a small ganglion and so on ; whereas in the other, 

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