Scientific Intelligence — Zoology. 381 



birds, about 8000 species are certainly known ; and to these we may 

 perhaps add 4000 for those not yet discovered, or not yet clearly dis- 

 tinguished. Of reptiles, about 1200 species are known ; but it is 

 probable that the proportion not yet discovered is larger, and that 

 for this we should add at least 800 species. Of fishes about 8000 

 species are known ; and to these, also, numerous additions may be 

 expected, probably at least 4000 species. Thus of verteb rated ani- 

 mals alone, nearly 19,000 species are known, and 9000 more are 

 probably in existence. The number of mollusks has been hitherto 

 reckoned chiefly by that of the shells contained in collections, no ac- 

 count being taken of any but the testaceous species. Of these about 

 15,000 species have been collected ; and probably at least as many 

 more yet t unknown to the conchologist. But the number of " naked'' 

 or shell-less mollusks is undoubtedly extremely large ; and of these 

 it is probable that only a small proportion are yet known.* The 

 class of insects far outnumbers all the preceding, both as to number 

 of species already known, and still more as to the number of whose 

 existence we have presumptive evidence. It is certain that at least 

 150,000 species are at present to be found in collections; and that 

 these do not by any means include the total number existing even in 

 the countries whose entomology has been best explored. So little, in 

 fact, is this the case, that if anything like the same proportion holds 

 good elsewhere between flowering plants and insects, as obtains in 

 our own country (namely at least ten species of insects to every species 

 of flowering plant), we should have to estimate the total number of 

 existing species of insects at little less than two millions. In regard 

 to none of the inferior classes, have we at present adequate means of 

 forming any estimate whatever. — (Carpenter's Principles of General 

 and Comparative Physiology, p. 239.) 



4. Dr Hamilton on the Guano Birds of the Lobos Islands.— 

 Along the sea-coast of Peru and Bolivia, within the tropic of Capri- 

 corn, countless numbers of aquatic fowls exist which live on fish, 

 and whose excretions are exceedingly fertilizing. In some localities, 

 the number of guanas is enormous, so that when alarmed by discharges 

 of fire-arms, or otherwise, they rise from their resting-places in such 

 masses as cannot be supposed by those who have never seen these 

 birds darkening the air like a cloud. Guano producers change their 

 habitation when continuously disturbed, but they do not permanently 

 leave a locality which has long been frequented by them in conse- 

 quence of a temporary alarm ; for, in such a case, they soon return 

 to their old haunts, and totally abandon them only when teased by 



* Thus, of the tribe of Nudibranchiate Gasteropods, only about a dozen species 

 were formerly known as inhabiting the coast of Britain ; but in the beautiful 

 monograph of Messrs Alder and Hancock (in course of publication by the Ray 

 Society), more than a hundred species will be described. 



VOL. LIV. NO. CV'III. — APRIL 1853. 2 C 



