IN THE ' BIOLOGIA CENTRALI-AMERICANA.' 549 



species referable to the Theromyiclag ; these are all small animals 

 and seem to have been A'^ery abundant, so that, like the rats and 

 mice of to-day, they would be especially liable to accidental trans- 

 port. The same may have been the case with the Insectivora. 

 What really happens when a land-bridge is established is well 

 shown in the intermingling of the faunas of Noi-th and South 

 America after the establishment of the Isthmus of Panama at the 

 end of the Miocene or beginning of the Pliocene period. 



Loi-d Rothschild, D.Sc, F.R.S., F.Z.S,, said that while in no 

 wsiy wishing to oppose the views of the speakers who preceded him, 

 he thought, and had always thought, that in many cases the sup- 

 posed relationship of the faunas of widely separated areas was more 

 apparent than real, and that many of the instances usually quoted 

 were cases of convergence or parallel development. This could be 

 easily explained if we considered that the chain of evolution of 

 all species owed its commencement to a stimulus dvie to the ex- 

 ternal environment the species found itself in, causing variation 

 to proceed in a cei-tain direction. It is also as easily conceivable 

 that a similar or even identical stimulus might start a chain 

 of variation along similar or even identical lines in two totally 

 different areas. He instanced among birds the two snipe, Galli- 

 oiago nohilis and macrodactyla, the former from South America, 

 while the latter inhabited Madagascar. These two birds are 

 practically identical, but had evidently had sepai-ate origins. He 

 also instanced the genus Mcenas among the Arctiid moths, 

 species being found in Africa, Indo-Malayana, and South Amei'ica. 

 While in the imago the structure was identical, in the larva the 

 difference in habits pointed clearly to a separate origin, for while 

 the larvee of the species inhabiting the Old World were terres- 

 trial the larvse of the South-American species were entirely 

 aquatic. On the contrary, he pointed out that the case of the 

 gigantic land-tortoises favoured the views of the previous speakers, 

 for while at present they were confined to two small groups of 

 islands, the Aldabra and Mascarene group in the Indian Ocean and 

 the Galapagos Islands off the South-American coast, in Miocene 

 times they were found in many parts of the world and the 

 present-day forms were merely survivals. 



Dr. R. Broom, D.Sc, C.M.Z.S. — When I was a student 30 years 

 ago the scientific world was so much under the spell of Russel 

 Wallace that any one who ventured to suggest the possibility of a 

 land-connection across what was regarded as a permanent ocean 

 was looked upon as a dangerous heretic, and even now there are 

 many who are apparently afraid to admit the possibility ; yet, if 

 there is one point on which we can be pei'fectly certain, it is 

 that South Africa was connected by land with South America in 

 Lower Permian times. Identical species of plants lived in the 

 two continents, and we know enough of the floras of North 

 Ameiica^ and Europe to feel sure that the species did not pass 



