— ee E 
See 
1891.] The Origin of the Galapagos Islands. 225 
of these islands we will find other species of Tropidurus. It 
would be of special interest to know whether any of them are 
found on Narborough, since we have to suppose that probably 
every organism was killed by that great eruption mentioned by 
Morrell. No other animal or plant shows the specialization of a 
single genus in the different islands so well as Tropidurus. On 
every or nearly every island it has developed into a different race 
or species. Let us now, for instance, compare the forms from 
Gardner and Duncan Islands with those from the nearest islands. 
On Gardner Island we find the same species as on Hood Island. 
Gardner is only one kilometer distant from Hood. The water 
between the two is not deep, not exceeding five fathoms. Between 
these islands are placed four smaller islets and the Magicienne- 
Rock (Brit. Adm. Chart, 1376). 
The species from Duncan Island is totally different from that of 
Indefatigable. The islands are only ten km. distant from each 
other. The deepest sounding taken between the two is, however, 
60 fathoms. No specimen of T. duncanensis occurs on the very 
near Indefatigable, and none of T. indefatigabilis on Duncan. The 
races from the distant Abingdon and Bindloe and the low Hood 
Islands are more different from the central forms than those among 
each other. 
Besides the genus Tropidurus, which is only found in South 
America, we have two other genera of Iguanide which are pecu- 
liar to the islands: the land and sea guanas, as called since the times 
of Dampier : Conolophus and Amblyrhynchus, the latter reaching 
a length of nearly four feet. 
Amblyrhynchus is the. only “ oceanic” form of the Iguanidz. 
It lives upon sea-weeds, and to get them it goes out to the sea, 
but never far from the shore. It is probably found on all islands. 
The “ Albatross” collected specimens on Abingdon, Duncan, 
Hood, Gardner, James, Chatham, and it has been recorded from 
other islands, Charles, Barrington, Jervis, Albemarle, by Darwin, 
Steindachner, Wolf, and others. The individuals of the different 
islands have never been studied carefully; but I do not doubt that 
even here we find modifications according to islands. a 
the thirteen specimens brought back by the “ Albatross” could 
