The Value of Fossils 331 



the offered solutions. The mere fact of palms having flourished in 

 Miocene Spitzbergen led to an h}"pothetical shifting of the axis of 

 the world rather than to the assumption, by way of explanation, that 

 the palms themselves might have changed their nature. One of the 

 most valuable aids in geological research, often the only means for 

 reconstructing the face of the earth in by-gone periods, is afforded by 

 fossils, but only the morphologist can pronounce as to their trust- 

 worthiness as v>'itnesses, because of the danger of mistaking analogous 

 for homologous forms. This difficulty applies equally to living groups, 

 and it is so important that a few instances may not be amiss. 



There is undeniable similarity between the faunas of INIadagascar 

 and South America. This was supported by the Centetidae and Den- 

 drobatidae, two entire " families," as also by other facts. The value 

 of the Insectivores, Solenodon in Cuba, Centetes in Madagascar, has 

 been much lessened by their recognition as an extremely ancient 

 group and as a case of convergence, but if they are no longer put 

 into the same family, this amendment is really to a great extent due 

 to their widely discontinuous distribution. The only systematic 

 difference of the Dendrobatidae from the Ranidae is the absence of 

 teeth, morphologically a very unimportant character, and it is now 

 agreed, on the strength of their distribution, that these little arboreal, 

 conspicuously coloured frogs, Dendrobates in South America, Mantella 

 in INIadagascar, do not form a natural group, although a third genus, 

 Cardioglossa in West Africa, seems also to belong to them. If these 

 creatures lived all on the same continent, we should unhesitatingly 

 look upon them as forming a well-defined, natural little group. On 

 the other hand the Aglossa, with their three very divergent genera, 

 namely Pipa in South America, Xenopus and Hymenochirus in Africa, 

 are so well characterised as one ancient group that we use their 

 distribution unhesitatingly as a hint of a former connection between 

 the two continents. We are indeed arguing in vicious circles. The 

 Ratitae as such are absolutely worthless since they are a most 

 heterogeneous assembly, and there are untold gi-oups, of the arti- 

 ficiality of which many a zoo-geographer had not the slightest 

 suspicion when he took his statistical material, the genera and 

 families, from some systematic catalogues or similar lists. A lament- 

 able instance is that of certain flightless Rails, recently extinct or 

 sub-fossil, on the islands of Mauritius, Rodriguez and Chatham. Being 

 flightless they have been used in supi)ort of a former huge Antarctic 

 continent, instead of ruling them out of court as Rails which, 

 each in its island, have lost the power of flight, a process which 

 must have taken place so recently that it is diificult, upon morpho- 

 logical gi-ounds, to justify their separation into Aphanapteryx in 

 Mauritius, Erythromachus in liodriguez and Diapliorapteryx on 



