28 ARKIV FÖR ZOOLOGI. BAND 3. N:0 3. 



onty reason why I do Dot think that the teeth ef the Oryc- 

 teropus have developecl to what they now are in such a way 

 as my friend Professor Weber suggests. If the ancestors of 

 the »xA.ard värks» once have had such speciahsed teeth with 

 folded enamel it must mean that also the animals themselves 

 have been rather speciahsed and had adapted themselves to 

 some certain kind of diet (herbivorous?) Avhich required this 

 kind of highly developed teeth. It seems then rather im- 

 probable that such animals first should have entirely changed 

 habits in such a way that the complicated structure of the 

 teeth no longer was needed, and in consequence of this redu- 

 ced, but then again after another complete change of diet the 

 teeth should be transformed and highly speciahsed in quite 

 another direction. 



It seems then more plausible to me to begin with a gene- 

 ralised type of mammal with rather simple teeth. If we then 

 assume that these animals became exclusively insectivorous, 

 the dentition would loose its value. The anterior teeth which 

 were in the way and hindered the free use of the lengthened 

 tongue would disappear completely and the others degenerate 

 so far that tliey only consisted of short cones which had 

 löst the enamel. Thus looking like the small rudimentary 

 crowns of the present Orycteropus (conf. fig. 9). When this 

 stage was reached, we have to assume some small change in 

 habit consisting therein that the animals for some reason or 

 the other begun to crush their prey before swallowing it. This 

 change of habit might perhaps have some connection with 

 the present custom to seek chiefly or raore and more exclu- 

 sively termites as food. It is possible that it was necessary 

 to crush and kill these insects because they might otherwise, 

 especially the soldiers with their formidable jaws, be injurious 

 to the interiör parts of the animal if swallowed alive. When 

 this new use of the teeth as crushing implements begun they 

 became stimulated to new growth. But as the crowns al- 

 ready had löst the enamel covering and become quite rudi- 

 mentary they were not capable of further development. The 

 roots again were not so strongly reduced and were provided 

 with a living pulp. The crushing action, the pressure on 

 the remains of the teeth. the roots and their pulps reacted 

 on them already before their growth ontogenetically was fi- 

 nished and stimulated to the producing of more material of 



