Au^. 12, 1875] 



NATURE 



297 



been thus stopped, a bog was formed called " La Mare 

 aux Songes," with an alluvial deposit varying in depth 

 irom three to twelve feet. The tortoise bones occur at a 

 depth of three or four feet, imbedded in a black vegetable 

 mould ; lighter coloured specimens are from the vicinity 

 of the springs. (Zool. Trans., vi. p. 51). Among these 

 bones I have distinguished four species, the more im- 

 portant characteristics of which may be particularised as 

 follows : — 



1. Testudo iriserrata. — Proximal half of the scapula 

 trihedral, with the anterior side convex ; acromium tri- 

 hedral, straight. Coracoid anchylosed to scapula at an 

 early stage of growth. Humerus moderately slender, 

 with the shaft flattened, and a deep hollow between the 

 head and tuberosities. Shaft of the ulna narrow, much 

 twisted. Ossa ilei short and broad ; transverse and 

 vertical diameters of pelvis subequal ; front part of pubic 

 bones abruptly bent downwards. Femur stout, with much 

 dilated condyles ; a deep and broad cavity between the 

 head and trochanters. 



2. Testudo iiiepta. — Proximal half of the scapula tri- 

 hedral, with the anterior side concave ; acromium com- 

 pressed, with the end curved. Coracoid never anchylosed 

 to the scapula. Humerus moderately slender, with the 

 upper half of the shaft trihedral, and without hollow be- 

 hind the head. Shaft of the ulna broad, not much 

 twisted. Ossa ilei narrow and long ; vertical diameter of 

 pelvis much exceeding in length the horizontal ; front part 

 of pubic bones gently declivous. Femur stout, with much 

 dilated condyles, and with a deep and narrow cavity 

 between the head and trochanters. 



3. Testudo leptocne)tns, sparsely represented, with a 

 scapulary similar to that of T. irises rata; ossa ilei of 

 moderate length and width, femur slender, with mode- 

 rately dilated condyles, and with a deep and broad cavity 

 between the head and trochanters. 



4. Testudo bflutonii, known from scapulary and hume- 

 rus only. The former bone is strongly compressed ; 

 acromium with the end curved, Coracoid not anchy- 

 closed to scapula. Humerus very stout, with the shaft 

 trihedral in its whole length, and without hollow behind 

 the head. 



C. The Rodriguez Tortoise.— The remains from Rod- 

 riguez which 1 'nave hitherto examined, and for which 

 I am indebted to M. Bouton and to the trustees of the 

 Glasgow Museum, consist of fragments of the cranium, 

 perfect cervical vertebrre, pelvis, and the larger leg-bones. 

 They indicate one of the best marked species of the 

 entire group, with a double alveolar ridge, and with the 

 neck and limbs of greater length and slenderness than in 

 any other species. The neural arch of the sixth nuchal 

 vertebra is perforated by a large ovate foramen on each 

 side close to the anterior apophyses. These perforations 

 were closed by membrane in the living animal, and evi- 

 dently caused by the pressure of the apophyses of the 

 preceding vertebra, the animals having had the habit of 

 bringing the neck in a vertical position, so that these two 

 vertebrai were standing nearly at a right angle. Some of 

 the bones are exceedingly large, larger than any of those 

 from the Mauritius, and must have belonged to mdi- 

 viduals of the size •f our large living male from Aldabra. 

 n._RouND-HEADED TYPE : T. itidica. 



To this type belong all the specimens with a nuchal 

 plate which have been deposited in British collections 

 within the last forty years, or which elsewhere have been 

 described or figured ; and more especially the Tortoises 

 from Aldabra. "Whether all these specimens have come 

 from this small group is impossible to say, as we know 

 very little or nothing of their history. Although I have 

 succeeded in bringing together a considerable number of 

 specimens, from which it would appear that also in this 

 much smaller division several races could be distin- 

 guished, I think it best to defer, for the present, the 

 detailed publication of the results of my examination 



which ere long may be supplemented or modified by im- 

 portant accessions. 



In conclusion we may ask whether the facts which I have 

 endeavoured to place before the readers of Nature are 

 more readily explained with the aid of the doctrine of a 

 common or manifold origin of animal forms. 



The naturalists who, with Darwin, maintain a common 

 origin for allied species, however distant in their habitats, 

 will account for the occurrence of the tortoises in the 

 Galapagos and Mascarenes in the same way as, for in- 

 stance, for the distribution of the Tapirs, viz., by the 

 hypothesis of changes of the surface of the globe. Taking 

 into consideration other parts of the Faunae, they would 

 have to assume, in this case, a former continuity of land 

 (probably varying in extent and interrupted at various 

 periods) between the Mascarenes and Africa, between 

 Africa and South America, and finally between South 

 America and the Galapagos. Indeed, the terrestrial and 

 freshwater fauna of Tropical America and Africa offer so 

 many points of intimate relationship, as to support very 

 strongly such a theory. The -Tortoises, then, would be 

 assumed to have been spread over the whole of this large 

 area, without being able to survive, long the arrival of 

 man or large carnivorous mammals. The former, espe- 

 cially before he had provided himself with missile 

 weapons, would have eagerly sought for them, as they 

 were the easiest of his captures yielding a most plentiful 

 supply of food ; consequently they were exterminated on 

 the continents, only some remnants being saved by having 

 retired into places which by submergence became sepa- 

 rated from the mainland before their enemies followed 

 them. With this hypothesis we would be obliged to con- 

 tend for this animal type an age extending over enormous 

 periods of time, of which the period required for the loss 

 of power of flight in the Dodo or Solitaire is but a 

 fraction. 



To my mind the advocacy"of an independent origin of 

 the same animal type, however highly organised, in 

 different localities, seems equally justified. It has been 

 urged that closely similar structures of the animal 

 organism have been developed without genetic relation- 

 ship ; so, also, the same complex organic compound, as 

 sugar, is produced normally by the plant and abnormally 

 by the human organism. Without overstepping too far 

 the limits of probability, we may assume that some Land- 

 Tortoises were carried by stream and current from the 

 American Continent to the Galapagos, and that others 

 from Madagascar or Africa, found in a similar manner a 

 new home in the Mascarene Islands. These tortoises 

 may originally have differed from each other, like the 

 Testudo tabulaia, radiata, [sulcata of our days, possibly 

 not exceeding these species in size, but being placed under 

 the same external physical conditions evidently most 

 favourable for their further development, they assumed in 

 course of time the same gigantic proportions and other 

 peculiarities, the modifications in their structure which we 

 observe now being partly genetic, partly adaptive. 



Thus this curious phenomenon in the geographical dis- 

 tribution of animals can be explained by either of those 

 two theories, and does not appear to me to strengthen the 

 position of one more than that of the other. The multi- 

 plicity of the races which I have pointed out above I need 

 not further discuss. As regards the Galapagos, this fact 

 is quite in accordance with what has been long recognised 

 in the distribution of the birds of the same archipelago, 

 and the co-existence of several races in Mauritius is per- 

 fectly analogous to the variety of species of Dinomis in 

 New Zealand. ALBERT GiJNTHER 



NOTES 

 Prok. ScHch^FELD, of Mannheim, has been appointed suc- 

 cessor to the late Prof. Argelander as Director of the Obser- 

 vatory at Bonn, and will enter upon his duties on Sept. I. Dr. 



