vi AUTHOR'S PREFACE 



remaining members. Anyone who reads through a full and exhaustive 

 examination of this kind, which endeavours to explain the causal con- 

 nection between the structure and the functions of living organisms, will 

 at once admit that instruction conveyed in this manner not only presumes 

 a much greater attention, a more careful observation, and more accurate 

 inferences on the part of the scholar, but also a much deeper comprehension 

 of Nature and natural phenomena than ever was or can be obtainable by 

 a mere description. Descriptions of the usual kind may be " read off" 

 by any pupil, even the youngest, under the teacher's guidance, either 

 from the natural object itself or a good illustration, and ought also to 

 be furnished by the scholar himself as an incentive to independent 

 activity on his part ; but, in my opinion, these ought not to find a place 

 in a school text-book. 



That the method here recommended of studying natural objects does, 

 however, by no means neglect the accurate observation of form and 

 character is evident from the fact that, when these are not recognised, 

 their significance also must remain unknown. 



A thoroughly sound instruction conducted on these principles must, 

 however, be based on direct observation ; and I have therefore in this 

 work, as far as was possible, selected types from our native fauna, and by 

 preference such as are of special importance to man and in the order of 

 Nature as a whole. This principle of selection has also been adopted in 

 the case of the other more briefly considered species. 



In my explanations, I have in places been obliged to make use of a 

 somewhat teleological manner of expression, it being impossible to express 

 relations of cause and effect pregnantly in any other form. Nor is it 

 necessary to remind teachers that the general data (to be worked out by 

 the teacher and pupil himself), viz., the definitions and characters of the 

 separate groups, have been placed as headings to the several sections 

 only in order to afford a convenient synopsis of the group and to avoid 

 repetition. 



I have endeavoured, even down to details, to shape my explanations 

 in accordance with the present status of the natural sciences, while at 

 the same time I have avoided reference to general theories not yet 

 fully substantiated or unintelligible to the young. Being fully conscious 

 that it is no longer within the powers of a single student to command 

 the whole wide domain of zoology, I have invariably in doubtful and 

 difficult cases called in the advice of distinguished specialists, which has 

 always been bestowed with the utmost readiness and goodwill". T 

 hereby, therefore, wish to express my warmest thanks to the gentlemen 

 who have thus kindly assisted me, viz. : Dr. Ahlborn, Hamburg ; Priv. 

 Decent Dr. Brandes, Halle-on-Saale ; Professor Dr. Dahl, Berlin ; Dr. 



