42 GENESIS OF THE ARIETID.E. 



among the Ammonites. This author, in his"Studien iiber die Stammesgeschichte 

 der Ammoniten," 1 traces the Armatus or Aspidoceras stock of the Upper Jura to 

 the Planulati ; that is, to the genera Coeloceras and Dactylioceras, which last I 

 had previously described and traced to an origin in Deroceras Dudressieri of the 

 the Lower Lias. 2 His work is a summary of evidently extensive observations 

 upon the Ammonites of the Upper Jura, all of which he traces directly or indi- 

 directly to the Planulati. Whether he can sustain this opinion will be questioned 

 by some until he has published his plates. He has, however, studied the series 

 according to proper methods of analysis, and should be given the credit of the 

 doubt. We also, though the author fails to notice the fact, have traced Pclloceras 

 athleta to the same species in the Lias, Amm. annulafus Quenst., and published the 

 remark 3 that they were genetically connected by intermediate forms. Our obser- 

 vations, therefore,- closely accord upon this very important species, and we also 

 agree in the view that most of the Jurassic genera we have included in the 

 Spinifera and Plicatifera can be traced to Coel. Pettos as the probable radical.* 



In his fourth chapter Wiirtenberger gives the history of the evolution of the 

 Lallierianus series, in which he traces degeneration in the lobes and saddles, 

 showing that changes of all kinds appear first on the outer (adult or senile) whorl 

 of the ancestral forms, and encroach more and more on the inner (3-ounger) 

 whorls in descendants. Neumayr 5 considers that Wiirtenberger was the dis- 

 coverer of the law of acceleration in development, and this author states that he 

 first published his new discoveries in " Ausland " of 1873, — about five years 

 after the appearance of precisely similar statements in such scientific periodicals 

 as the Proceedings of the Philadelphia Academy, by Professor Cope, and the 

 Proceedings and Memoirs of the Boston Society of Natural History, 6 by the 

 author. Professor Cope has lately republished his discoveries in a volume en- 

 titled " The Origin of the Fittest," and in these masterly essays those who are 

 interested may get a full view of his mode of explaining this law, and will find 

 very complete series of illustrations of the character and meaning of parallel 

 series and other related phenomena. 



The decision as to who discovered the law of acceleration is only historically 

 interesting; but it is of general importance that so many persons agree, and 

 that an eminent paleontologist like Neumayr, who has studied such phenomena 

 among fossils, considers the law to be true in its application, as tested by him, 

 with some exceptions. He does not state the exceptions, however, and they 

 cannot be discussed. The opinions of Wiirtenberger and Neumayr that some 

 species inherited characteristics at later stages than those in which they occurred 

 in any ancestral species or pair, seem at present to rest upon the insecure basis 

 of the apparent need of this assumption in order to account for acceleration as 



1 Ernst Gunther, Leipzig, Darwinistische Schriften, No. 5. 



2 Non-reversionary Series of the Liparoceratidse, etc., Proo. Bost. Soc. Nat. Hist., January, 1872, and 

 Appendix to the same, with a geological table, Ibid., May 20, 1874. 



3 Proc. Bost. Soc. Nat. Hist., Appendix to Non-reversionary Series of the Liparoceratidre, 1874, p. 33. 



4 See above, pp. 23, 24. 



6 Zeitsch. d. deutsch. geol. Gesellsch., p. 868. 



6 See above, page 28, note 3, and Proc. Bost. Soc. Nat. Hist., 1870, pp. 72, 73. 



