So SCIENCE PROGRESS. 



centralia in the carpus, and formulates the known 

 variations of the carpal elements in general ; and he 

 incidentally describes an occasional cleavage of the 

 innermost digit, and the convergent resemblances be- 

 tween the Cetacean and Ichthyosaurian paddles. The 

 interest of this topic has since vastly increased during 

 the study of the Crocodilia ; for Kukenthal himself 

 has shown 49 that the fourth and fifth digits of these 

 animals, vestigial in the adult, are in the embryo hyper- 

 phalangeal. From this discovery he deduces a belief in 

 their origin from more completely aquatic, and probably 

 marine, ancestors, of intense interest in its bearings upon 

 Rose's recent inquiry 50 into their tooth-genesis. It seems 

 not a little significant under this head to reflect on the 

 striking similarity, presumably due to mere convergence 

 under adaptation to a similar mode of life, which the 

 rostra and teeth of the Cetacean Platan ist 'a and the 

 Crocodilian Gavialis, living side by side in the Ganges, 

 present. 



The third chapter, written conjointly with Dr. Theo- 

 dor Ziehen of Jena, deals with the nervous system, and 

 more especially the homologies of the brain convolutions 

 in these animals and the Pinnipedia, as compared with 

 those of the leading orders of placental mammals ; and the 

 authors' conclusions 61 are considerably at variance with those 

 of Turner, published two years later, in apparent ignorance 

 of their w r ork. The authors deduce four laws of develop- 

 ment and variation of brain convolution, and an allied 

 section of the work is devoted to the sense organs, the 

 nasal organ of the Cetacea on comparative embryological 

 grounds being reduced to that of the ordinary mammalian 

 type. The detailed facts recorded, receive a welcome 

 corollary in Hill's 52 recent assertion that the fascia dentata 

 and olfactory bulb are correlatively variable with each other 

 and the olfactory organ, and in this section the conclusion 

 is emphasised that the Cetacea of to-day may be a 

 diphyletic assemblage — a conclusion of no little moment, 

 in relation to current belief in a similar origin for other 

 great groups of living animals of high structural organisation. 



