170 GALAPAGOS ARCHIPELAGO. 



markably arborescent genus of the CompositcB, is 

 confined to the archipelago. It has six species : 

 one from Chatham, one fi'om Albemarle, one from 

 Charles Island, two from James Island, and the 

 sixth from one of the three latter islands, but it is 

 not known from which : not one of these six spe- 

 cies grows on any two islands. Again, Euphor- 

 bia, a mundane or widely-distributed genus, has 

 here eight species, of which seven are confined to 

 the archipelago, and not one found on any two isl- 

 ands ; Acalypha and BoiTeria, both mundane gen- 

 era, have respectively six and seven species, none 

 of which have the same species on two islands, 

 with the exception of one BoiTeria, which does oc- 

 cur on two islands. The species of the Composi- 

 ta3 are particularly local, and Dr. Hooker has fur- 

 nished me with several other most striking illus- 

 trations of the difference of the species on the (Af- 

 ferent islands. He remarks that this law of distri- 

 bution holds good both with those genera confined 

 to the archipelago and those distributed in other 

 quarters of the world : in like manner, we have 

 seen that the different islands have their proper 

 species of the mundane genus of tortoise, and of 

 the widely - distributed American genus of the 

 mocking-thrush, as well as of two of the Galapa- 

 geian sub-groups of finches, and almost certainly 

 of the Galapageian genus Amblyrhynchus. 



The distribution of the tenants of this archipelago 

 would not be nearly so wonderful, if, for instance, 

 one island had a mocking-thrush, and a second 

 island some other quite distinct genus ; if one isl- 

 and had its genus of lizard, and a second island 

 another distinct genus, or none whatever ; or if the 

 different islands were inhabited, not by representa- 

 tive species of the same genera of plants, but by 

 totally different genera, as does to a certain extent 



