Bihliographtcal Notice. 418 



BIBLIOGRAPHICAL NOTICE. 



Allyemeine Zoologie, oder Grundrjesetze des thierischen Baits mid 

 Lebens, von H. Alexander Pagenstecher. Erster Theil. 8vo. 

 Berlin : Wiegaudt, Hempel, and Paiey, 1875. 



The book promises to be one of the best text-books of the principles 

 of zoology that we possess. Its author is in favour of the doctrine 

 of the origin of species by evolution ; but this does not hinder his 

 giving a most impartial statement of the facts and inferences upon 

 which a philosophical zoology must be founded. The general prin- 

 ciple upon which he has worked may be expressed as follpws in 

 his own words : — " Xatiire can only be described. Explanatioi.s, 

 the establishment of causalities and pur[3oses, mechanical, dynamical, 

 monistic, and dualistic systems are attempts at the desciiption of 

 nature. The most useful of them will be that which furnishes the 

 most complete result in the simplest and most easily intelligible 

 way." 



Starting from this view of the natural-history problem. Prof. 

 Pagenstecher describes in his second book the properties of animal 

 bodies in general, commencing with the ultimate simple constituents 

 of the bod}', passing to the combination and differentiation of these 

 constituents to form composite living bodies, then discussing the 

 idea of animal individuality and polymorphism (or, as he calls it, 

 pleomorphism), and, finally, the morphological arrangement of the 

 parts of which the bodies of animals are composed. The arrange- 

 ment and treatment of the matter in this book makes it an admirable 

 summary of the broad princii)les of animal morphology. 



In the third book (the last in the part now before us) the author 

 treats of the limitation and classification of the animal kingdom ; and 

 this leads him to give an historical account of the doctrine of the 

 species from the earliest periods to the present day. His conclu- 

 ding remarks upon this subject are excellent, and show strikingly 

 the moderation of his tone. He says : — " There is no doubt that 

 species are not eternal, and that they are variable. The duration of 

 the individual species with all their peculiarities, or even the duration 

 of a part of the specific peculiarities, siich as finds expression in the 

 characters of genera or families, and therefore the duration of genera 

 or families, is very unequal. Some are long-lived, others not, with- 

 out one being able to see the causes of this clearly from the sur- 

 rounding conditions. The changes which have occurred in the ap- 

 pearance of the animal and vegetable world in the course of the 

 geological epochs agree with what we know of changes })y varia- 

 bility, of nietamor|)hoses in dcvelo]>mental hiHtory, and of difference 

 in nearly allied forms ; but they go beyond those. At least much in 

 the fossil forms stands for the present uncoml)ined with the living. 

 The action of external circumstances ujxni the form and structure 

 of animals has not yet been sufficiently investigated ; in all cases 

 there is in opposition to their consequences a very ])owerful agent, 

 which we name specific persistence." These views arc further de- 



