220 



NATURE 



{Jan. 22, 1874 



some cases, help botanists to account for the presence of 

 the many curious and apparently useless glands and 

 appendages plants often possess. 



Among other natural history information in this work, 

 we find some excellent observations on reasoning power 

 in insects, a good description of the habits of a monkey, 

 and some judicious remarks on the mode of action of 



Fig. I. — Leaf of I\IcIastoma. 



natural selection ; although the idea that the hairless 

 breed of dogs has been produced because hair favours 

 the increase oi pediculi and other parasites, is hardly one 

 that will be accepted, seeing that hairless forms, of carni- 

 vora at all events, are quite unknown in a state of nature. 

 On the subject of the fertilisation of flowers by insects 

 Mr. Belt remarks, that besides the special adaptations for 



2. — Flower of ^Iarcgravia nepenlholdes. 



fertilisation by certain insects, there are often other adap- 

 tations for the express purpose of preventing useless 

 insects from robbing the flowers of the attractive nectar, 

 and he illustrates this by a description of our common fox- 

 glove. He also furnishes, what I believe are new and very 

 curious cases of fertilisation by birds. In the Marc^mvia 

 ncpcnlhoidcs (Fig. 2) there is a group of pitchers below 



the flowers, containing a sweet liquid which attracts in- 

 sects ; and numerous insectivorous birds come to feed 

 upon these insects, and in doing so necessarily brush off 

 the pollen and convey it to other flowers. In a species 

 of Erythrina having a sword-shaped flower which will 

 only admit very minute insects to the nectary, two species 

 of long-billed humming birds probe the flowers in search 

 after the insects, and in doing so get the pollen on their 

 heads and carry it to other flowers. In this case the 

 nectar is protected by a thick fleshy calyx, which effectu- 

 ally prevents bees and wasps from breaking in and steal- 

 ing the attractive liquid. 



As a geologist our author contributes some important 

 facts on the great question of an intertropical glacial 

 period. He found at from 2,000 to 3,000 feet above the 

 sea, an extensive formation of boulder clay, full of great 

 angular blocks, which he has not the slightest hesitation 

 in pronouncing to be of glacial origin. He decides that 

 this formation must be due to land glaciers and not to 

 icebergs, because the latter would imply a depression of 

 the country fully 3,000 feet, which would have produced a 

 wide channel connecting the Atlantic and Pacific, and 

 have caused more intermingling of the faunas of the 

 two oceans than actually exists. It may, however, be 

 argued, on the other hand, that if there has been no 

 recent communication between the two oceans, then 

 scarcely a single species of fish or mollusc should 

 be common to the two. Yet no less than 48 

 species of fishes are absolutely identical ; and as to the 

 molluscs, Mr. P. P. Carpenter says that, besides those 

 undoubtedly identical (about 40), more than 30 others 

 may be identical, and that 40 more, although distinct, 

 are very close representative species. We have, there- 

 fore, over 100 species of molluscs so nearly identical in 

 the two oceans, that we cannot suppose their separation 

 to date longer back than the PUocene period. It may be 

 fairly argued that this amount of community proves 

 a connection between the oceans at a recent date, 

 and that the number of species in common is quite 

 as great as we can expect, when we consider — firstly, 

 that migration into an already fully stocked area is 

 by no means so easy and rapid a process as was 

 once supposed ; and secondly, that the presence 

 of icebergs depositing their loads of clay and gravel in 

 the straits themselves would, perhaps, destroy most forms 

 of marine life, or drive them away to some distance. 

 Mr. Belt further advocates, what seems a very untenable 

 theory, that the glacial period of the northern and 

 southern hemispheres was at its greatest severity at the 

 same time, and that the glacial deposits of Central Ame- 

 rica and Brazil are synchronous. To get over the enor- 

 mous difficulty as to what became of the exclusively 

 tropical forms of insect and bird life that abound in such 

 overpowering luxuriance in tropical America, he has re- 

 course to the increased area of low land caused by the 

 lowering of the ocean owing to the vast amount of water 

 abstracted in the form of ice. But Mr. Andrew Murray's 

 map of the 100 fathoms line of soundings shows that the 

 tropical part of South America would not be materially 

 increased in area by a depression of 600 ft., and another 

 600 ft. would add proportionately less. Besides, if astro- 

 nomical causes have produced glacial epochs, it is certain 

 that they would occur alternately in each hemisphere ; 



