No. 594] 



NOTES AND LIT EE ATTIRE 



381 



They are intended only as a rough index of the degree of probability 

 that attaches to the method, and to show that the populating of the 



rafts, is not an explanation to be set aside as too unlikely for c.n 



I confess to some haziness as to the probabilities here set forth, 

 but, if they are anywhere near true, entomologists need not 

 worry. In addition to their creatures not needing rafts as badly 

 as do mammals, it is certainly probable that every, not "one in a 

 hundred," natural raft big enough to be noticed and recorded 

 by voyagers contained not one, but many, insects. Smaller rafts 

 or even single trees might contain many individuals of several 

 species and, since a sin-le fertilized female gives birth to many 

 offspring, the chance of a given species establishing itself on 

 virgin soil is much greater than it is in the case of mammals. 

 Furthermore, insects have been dispersing since before the Car- 

 boniferous. Many of the islands may not be that old, but this 

 simply means that insects have had a chance at such an island 

 since the first wavelets rippled about its uplifting peak. The one 

 thing which may be comparatively disadvantageous to insects is 

 that many of them are rather closely bound up in their food re- 

 lations with certain plants, but this disadvantage is somewhat 

 decreased by the fact that, if phytophagous insects are carried 

 on natural rafts, their food plant is likely to be a part of the 

 material which makes up the raft and both may be established 

 together. The pros and cons are numerous and involved. It is a 

 balancing of probabilities with the burden of proof on the side 

 which claims the right to make over major features of the earth's 

 surface in the face of contrary geological evidence. 



If this be true for the scant fauna of oceanic islands, what shall 

 we say of the suggested bridges, running this way and that, 

 across the oceans for the purpose of connecting continental 

 faunas and floras, especially in equatorial regions? Mercator 

 gave us a map of the world so constructed that the longitudinal 

 lines are parallel from the north pole to the south. Now the fact 

 is that a degree of longitude equals approximately 111,300 

 meters at the equator. 104,600 meters at 20° latitude, 85.400 

 meters at 40°. 55,800 meters at 60°. 19,400 meters at 80°, and no 

 meters at the poles. Therefore the equatorial distances on Mer- 

 cator 's projection are relatively far too short. On the globe or 

 on a proportional projection in which a meter at the equator is 

 as long as a meter in Alaska we see that north of the Tropic of 

 Cancer in the eastern hemisphere lies a huge land mass consist- 



