DE. E. EAY LANKESTEE ON OKAPIA. 297 



The caducitliecal caviconi of AnUlocapra is, it seems, the sole modern example of 

 the combination of horny theca with branched or prong-bearing form. If we assume 

 that, starting from conditions more or less closely similar to those exhibited by the 

 vellericorns of Giraffa, there was, so to speak, a demand for a large branched prong- 

 bearing horn, there would be two alternative modes of meeting the demand. The 

 integument might be left unprotected and soft on the growing antler, in which case it 

 would tend to be seriously damaged and torn by blows, or it might be protected by a 

 theca, periodically shed and renewed. A periodicity in the nutrition of the horn- 

 structures would be established in the latter case. In the former case the exposure of 

 the bony mesoblastic tissues by abrasion of the integument would tend to necrosis of 

 the bone and serious danger to the animal. It would thus be an advantage that the 

 exposed dead bone of the antler should be shed and a new formation take place at 

 intervals. The establishment of a relation between this and the nutritional activity of 

 the recurring annual process of sexual ripening is not an improbable thing. The 

 periodicity of the horn-shedding of the caducithecal forms and that of the antler- 

 shedding forms may well have had a common origin. 



The antlers of Cervidse seem thus to be an outcome of the simple short vellericorns 

 still retained by the Giraffe, and the three structures — viz. unbranched Cavicorns, 

 Caducithecal Prong-horns, and naked regenerative Antlers — are three distinct lines of 

 development of Pecorine horns of increased strength, amplitude, and resistance, from 

 conditions present in ancestral GirafSdge. These varieties of horn-structure were 

 probably more or less completely differentiated within that group, or in a more 

 generalized set of forms antecedent to it. 



Whilst thus referring the various forms and structures of Pecorine horns to primitive 

 conditions retained by GirafSdse, I do not overlook the fact that in regard to other 

 important structures the Giraffidse do not exhibit archaic features. The great length 

 of the diastema in the dental series and the complete absence of upper canines are 

 points in which GirafHdse are not primitive, as also is the total suppression of the 

 pettitoes. In possessing often well-developed, even extremely large, canines the 

 Cervidae are more primitive than the Giraffidae ; and both Cervidse and most Bovidse, in 

 the frequent presence of well-developed extra digits, retain an ancestral feature lost 

 by Giraffidse. There is, however, ample ground for supposing that in the differentiation 

 of lines of descent from the primitive Pecora one group may have retained one set of 

 characters in a primitive condition and another group another set. 



1 propose now brietiy to revert to the Okapi's skull and its " bosses '' or 

 " tumescences." It is, of course, possible, as our larger specimen is only two-thirds 

 grown, that a separate " ossicusp " was destined to develop over each of the supra- 

 orbital bosses {otl. in text-fig. 2, p. 284). There does not appear to have been any 

 rudiment of such a structure in the dried skin of the head as removed by the 



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