viii PREFACE. 



proportions of the remiges and rectrices, leaving all the rest unnoticed. So also as regards the 

 parasites : these were at first hardly more than ballast, which, from the want of other lading, he 

 would not at once throw overboard; but subsequently finding them present so many points of 

 interest, he occupied himself with them specially for a time. This mode of investigation he 

 appears to have continued from the commencement of the present century, when it was begun 

 (for I have now before me manuscripts of the year 1800) to about the year 1812 or 1813. During 

 this period, his memoirs in ' Voigt's Magazin' -and his ' Osteographische Beitrage' were pub- 

 lished, the only samples of his investigations which he laid before the public. But from this 

 time, and especially after his establishment in Halle, his activity acquired a different character. 

 Becoming now better acquainted with the recent progress of Zoology, and with the requirements 

 of that department which he had particularly selected for his own study, he saw that every special 

 and exact investigation only attains a permanent and true value when it stands, not merely as 

 an isolated contribution to the enlargement of our knowledge of the subject, but when it is at the 

 same time brought into its proper connection with the totality of the other properties of the objects 

 investigated, and the precise limits are indicated within which it is a criterion of form, furnishes a 

 modification of the typical fundamental idea, and thus assists in characterising the method of modifi- 

 cation. From this moment, every partial publication of this or that peculiarity lost all value in his 

 eyes ; and when he could not at once say precisely where it occurred, how far it extended, and 

 what was indicated and excluded by it, he preferred leaving it entirely unpublished. We find him, 

 therefore, scarcely ever coming forward except when compelled, either to extend one of these 

 isolatedly published facts to its natural limits, or to refer back to their proper connection pheno- 

 mena which had been drawn away from it. Only once afterwards did he surprise the zoological 

 public with a work which stands perfectly complete within itself, was entirely elaborated by himself, 

 and appears altogether so thoroughly worked out, that no results remain for his successors to add 

 to it. This publication was his work on the insects parasitic on animals, contained in the 

 third volume of Gennar's ' Magazin der Entomologie/ which furnishes an astonishing proof 

 of the care and perseverance with which he had studied the parasites of his favorites, although 

 these could only have been of subordinate interest to him. In its condensed brevity, it 

 is the best and most comprehensive monograph to which the literature of Entomology can 

 point. 



When he had thus, as it were, despatched the third part of his task, and freed himself from 

 it, he was able to devote himself with so much the more energy to the two remaining parts. And 

 this he did completely, only noticing the parasites when a new bird brought him a new form. 

 These he subsequently described, although in very few words, but never figured nor examined 

 particularly. With regard to the anatomical and pterylographical portions of his ornithological 

 studies, it was at first 'by no means Nitzsch's intention to elaborate them separately. In his view 

 both of these were merely means by which one of the highest objects was to be attained, namely, 



