158 



Dr. W. Kowalevsky on the 



[Feb. Q, 



of the same family, which in England proved to be associated with the tetra- 

 dactyle genus. To this new genus of the Hyopotamoid family I gave the 

 name Diplopus. This was indeed a welcome discovery — ancestor and de- 

 scendant existing together, the complete with the reduced form living 

 about the same period*. Moreover, the didactyle form bore a great general 

 likeness in the structure of the limbs to Anoplotlierium and Xiphodon, 

 being perhaps only a little more elaborate and better adapted than these 

 first experiments of the Eocene times. 



The likeness of the descendants allowed me to make inferences as to 

 the likeness of the ancestors ; and, taking into consideration the structure 

 of the limbs in the tetradactyle Hyojpotamus, and the rudimental second 

 and fifth digit still existing in Anoplotherinm, Xiphodon, and Hyojpotamus, 

 I feel confident that the supposed ancestor of the first two did really 

 possess a manus and pes very like the projected typical diagram; indeed 

 we may be nearly as confident of this as if we had found the actual thing 

 imbedded complete in some early Eocene or even Cretaceous rock. 



This, then, was the state of things in the earliest Eocene ; large numbers 

 of Paridigitata with tetradactyle feet like our Hyopotamus, and the 

 supposed progenitors of Anoplotherium and Xiphodon, represented the 

 group of Paridigitates with crescentic teeth (Selenodonta). Reduction in 

 the number of digits, being an advantage to the organism, was steadily 

 going on. But, be it observed, we follow now the hmdaptive line of 

 descent ; and while the whole weight of the body was, by gradual steps, 

 entirely transferred to the two middle digits, these thickened and grew 

 larger, but entered into no special adaptation by means of which they 

 should better perform the work which had fallen to their share ; they 

 did not enlarge so as to gain additional support from all bones of the 

 second row of the carpus and tarsus ; the reduction was inadaptive : 

 inheritance is in them stronger than modification. 



Seeing that old Paridigitata present only two free metacarpals and 

 metatarsals, and that recent Euminantia have the same two metacarpals 

 and metatarsals coalesced into a single canncnbone, evolutionists generally 

 rush at the seemingly obvious conclusion that once the tetradactyle foot 

 reached the reduced state of two digits, these coalesced together, and were 

 transformed into the cannonbone of Bum iu ants. No such thing, however, 

 happened ; nor could it have happened with the old didactyle Paridigitata, 

 as the Anoplotherium, Xiphodon, and Diplopus ; and the reason why it 

 could not is clearly indicated by the structure of their feet. We have 

 already shown that, f ollowing this inadaptive reduction, the two middle 

 digits, whilst growing larger, continue to occupy only the inner half or 

 more of the unciform and the greater part of the os magnum ; so that 

 from the outer as well as from the inner side the carpal bones which sup- 

 port useless rudiments overhang the two middle functional digits. In con- 



* Such cases are numerous. In the Sewalik Hills the Hipparion is associated with 

 the horse. 



