METAMORPHOSIS OF AMMONITES. 97 



Any one who, like myself, has had occasion to trace a 

 great number of these fossils through several strata of 

 considerable extent and thickness, and to handle hun- 

 dreds cf every species as heretofore classified, must 

 often have been astonished, to see how wide is the 

 divergence in many of these species. Often he must 

 have lost all hope of ever arriving at a clear delimita- 

 tion of species; again and again must he have felt less 

 inclined to dismiss the idea put forward by Darwin, 

 ' that our species are in fact only an artificial concept, a 

 mere formula.' Kayser consequently finds himself com- 

 pelled to adopt purely artificial limits, and speak of 

 ' Form-series,' as other writers do of Ammonites. Waagen 

 reminds us that, long before Darwin, Queenstedt had 

 suggested the Genetic connection of successive forms in 

 geological strata, and he then says : " There are but 

 few among the Palaeontologists who have recently 

 studied the Ammonitidae under the light of the Theory 

 of Descent, to whom the facts have not brought convic- 

 tion. The existence of Form-series, such as have been 

 shown again and again by late investigators series in 

 which each more recent form deviates but slightly from 

 its precursor, till the sum total of these small divergences 

 results in a wide dissimilarity from the original species 

 points with coercive clearness to the assumption of Genetic 

 connection." 



Zittel and Neumayr are of the same mind. Neumayr 

 writes : " There is hardly any fact which speaks so 

 conclusively for the validity of the Theory of Descent as 

 the existence of Form-series, which has been proved in 

 many cases, and of which more instances will certainly 

 be found now that attention has been directed to the 

 matter. A peculiarly beautiful example is to be seen 



