BEVIEW OF SOOES. 



Outlines of Comparative Physiology, etc.— 



By Louis Agassiz and A. A. Gould. 



[second notice.] 



As we have before commented on this 

 very admirable book, and promised, at an 

 early day, to give our readers a profitable 

 advantage from our labors in its perusal — 

 we now detach some miscellaneous passages, 

 all bearing upon the legitimate objects of our 

 London Journal in this particular depart- 

 ment ; and tending to make the inquiring 

 mind thirst for more knowledge from the 

 fountain head. Knowledge is the only thing, 

 perhaps, of which we cannot possess too 

 much ; for it does not " perish in the using." 



Let us first glance at the powers inherent 

 in us by an especial gift, and which, as being 

 " reasonable " creatures, are vested in us 

 alone. We will then, pari passu, take a peep 

 into this our lower world: 



Man, in virtue of his twofold constitution, the 

 spiritual and the material, is qualified to com- 

 prehend Nature. Having been made in the spi- 

 ritual image of God, he is competent to rise to 

 the conception of His plan and purpose in the 

 works of Creation. Having also a material body, 

 like that of animals, he is prepared to understand 

 the mechanism of organs, and to appreciate the 

 necessities of matter, as well as the influence 

 which it exerts over the intellectual element, 

 throughout the whole domain of Nature. 



The spirit and preparation we bring to the 

 study of Nature, is not a matter of indifference. 

 Vfhen we would study with profit a work of lite- 

 rature, we first endeavor to make ourselves ac- 

 quainted with the genius of the author ; and in 

 order to know what end he had in view, we must 

 have regard to his previous labors, and to the 

 circumstances under which the work was exe- 

 cuted. Without this, although we may perhaps 

 enjoy the perfection of the whole, and admire the 

 beauty of its details, yet the spirit which pervades 

 it will escape us, and many passages may even 

 remain unintelligible. 



So, in the study of Nature, we may he as- 

 tonished at the infinite variety of her products, 

 and may even study some portion of her works 

 with enthusiasm, and nevertheless remain stran- 

 gers to the spirit of the whole, ignorant of the 

 plan on which it is based; and may fail to ac- 

 quire a proper conception of the varied affinities 

 which combine beings together, so as to make of 

 them that vast picture, in which each animal, 

 each plant, each group, each class, has its place, 

 and from which nothing could be removed with- 

 out destroying the proper meaning of the whole. 



It is but a short time since- it was not difficult 

 for a man to possess himself of the whole domain 

 of positive knowledge in Zoology. A century 

 ago, the number of known animals did not ex- 

 ceed 8000; that is to say, in the whole Animal 

 Kingdom, fewer species were then known than 

 are now contained in many private collections 

 of certain families of insects alone. At the pre- 

 sent day, the number of living species which 



have been satisfactorily made out and described, 

 is more than 50,000. 



The number of vertebrate animals may be 

 estimated at 20,000. About 1500 species of 

 mammals are pretty precisely known, and the 

 number may probably be carried to about 

 2000. 



The number of birds well known is 4 or 5000 

 species, and the probable number is 6000. 



The reptiles, like the mammals, number about 

 1500 described species, and will probably reach 

 the number of 2000. 



The fishes are more numerous; there are from 

 5 to 6000 species in the museums of Europe, and 

 the number may probably amount to 8 or 

 10,000. 



The number of mollusks already in collections, 

 probably reaches 8 or 10,000. There are col- 

 lections of marine shells, bivalve, and univalve, 

 which amount to 5 or 6000 ; and collections of 

 land and fiuviatile shells, which count as many 

 as 2000. The total number of mollusks would 

 therefore probably exceed 15,000 species. 



Among the articulated animals it is difficult 

 to estimate the number of species. There are 

 collections of coleopterous insects which number 

 20 to 25,000 species ; and it is quite probable, 

 that by uniting the principal collections of insects 

 60 or 80,000 species might now be counted ; for the 

 whole departmentof articulata,c ^uprising the Crus- 

 tacea, the cirrhipeda, the insects, the red-blooded 

 worms, the intestinal worms, and the infusoria, 

 as far as they belong to this department, the 

 number would already amount to 100,000; and 

 we might safely compute the probable number of 

 species actually existing at double that sum. 



Add to these about 10,000 for radiata, echini, 

 star-fishes, medusa?, and polypi, and we have 

 about 250,000 species of living animals; and sup- 

 posing the number of fossil species only to 

 equal them, we have, at a very moderate com- 

 putation, half a million of species. 



The fossils already described exceed 6000 

 species; and if we consider that wherever any 

 one stratum of the earth has been well explored, the 

 number of species discovered has not fallen below 

 that of the living species which now inhabit any 

 particular locality of equal extent, and then bear 

 in mind that there is a great number of geologi- 

 cal strata, we may anticipate the day when the 

 ascertained fossil species will far exceed the 

 living species. 



These numbers, far from discouraging, should, 

 on the contrary, encourage those who study 

 Natural History. Each new species is, in some 

 respects, a radiating point which throws ad- 

 ditional light on all around it ; so that as the 

 picture is enlarged, it at the same time becomes 

 more intelligible to those who are competent to 

 seize its prominent traits. 



To give a detailed account of each and all of 

 these animals, and to show their relations to each 

 other, is the task of the Naturalist. 



Every well-educated person is expected to have 

 a general acquaintance with the great natural 

 phenomena constantly displayed before his eyes. 

 A general knowledge of man and the subordi- 

 nate animals, embracing their structure, races, 

 habits, distribution, mutual relations, &c., is cal- 

 culated not only to conduce essentially to ou 



