Remarks on the Descent of Animals. 141 



my opponents, that they shall carefully consider the exact ' em- 

 pirical proof here brought forward for them, as they have ao 

 eagerly demanded. May they, however, spare me the empty, 

 though by even respectable naturalists the oft repeated phrase, 

 that the monistic nature-philosophy, as expounded in the ' Gren- 

 eral Morphology,' and in the ' History of Creation,' is wanting in 

 actual proof. Precisely that exact form of analytical proof, which 

 the opponents of the direct theory demand is to be found, by any- 

 body who wishes to find it, in the ' Monograph of the Calcareous 

 Sponges.'" "This mutability of the Spongiadte" adds Oscar 

 Schmidt, " affords the extremely important evidence that, so to 

 speak, an entire class has even now, not attained a state of com- 

 parative repose." But to prove the variability of species satisfac- 

 torily, " the transition of the forms succeeding one another his- 

 torically in the strata of the earth" must be shown. 



The researches o£ "Waagen, Zittel, Neumayr and Wiirtenberger 

 have proven, in the most conclusive manner, "at least with 

 respect to che important division of the Ammonites, the utter im- 

 possibility of separating them into species." " Neumayr is such a 

 cool and cautious observer, that he allows nothing to pass current, 

 but that which is absolutely certain." It is true he holds it to be 

 " extraordinarily probable, that in all forms these gradual trans- 

 itions have taken place, yet in one case only does he demand un- 

 qualified assent; namely, that he has proven ' that Perisphinctes 

 aurigerus of the Bathoniaus, and Perisphinctes curvirostris of 

 the zone of the Cosmoceras Jason, are connected in such a man- 

 ner by intermediate occurrences that it is impossible to draw a 

 limit.'" 



Wiirtenberger's studies were applied to thousands of specimens 

 from the groups of the Planulate Ammonites, with ribbed shells, 

 and of the Arraate Ammonites with prickly shells. In summing 

 ■up his results he says : " In groups of fossil organisms, in which, 

 as in the present case, so many connecting links between the most 

 extreme forms are actually before us, that the transition is regu- 

 larly carried on, the species is far less susceptible of apprehension 

 than in the organic forms of the present world, which at least de- 

 note the existing limits of the great pedigree of the organic world. 



