20 MUSEUM OF COMPARATIVE ZOOLOGY. [Apr.' 



be thus retained is to depend upon the number on hand, and 

 the rarity or value of the specimens themselves. In making 

 this selection it is to be remembered, that a sufficient number 

 of specimens be set aside to complete the faunal collections as 

 well as the embryonic collections and the general systematic 

 collections. After this selection is made, the remaining speci- 

 mens may be considered as duplicates, and from these the 

 materials for anatomical studies may be taken. 



" Second. The anatomical preparations ought always to bear 

 upon the principles of classification. In a zoological museum, 

 such investigations are not designed to elucidate questions of 

 physiology, but to facilitate the study of zoological affinities, 

 and to establish on a more permanent basis the relative stand- 

 ing of the different kinds of natural groups among animals. 

 The anatomical preparations, made in the Museum, ought 

 therefore to elucidate as much as possible the characters of the 

 classes for themselves ; next those of the orders, that we may 

 learn to discriminate between class and order ; next those of 

 the families, the genera, etc. You will soon perceive, in con- 

 sulting zoological works, with reference to your labors in the 

 Museum, that there is not, to this day, a systematic classifi- 

 cation of animals in which this distinction of characters is 

 carried out. It will tend to remove much that has been arbi- 

 trary in Zoology thus far, if on studying the structure of 

 animals, we keep in mind the unequal value of structural 

 features. 



" As a special point of study, in the class of Mammals, I 

 would particularly urge the making of serial preparations of 

 the teeth, in every stage of growth of all the species sufficiently 

 common to afford the necessary materials. In like manner 

 should entire specimens of all the common species be set aside, 

 representing all their stages of growth from the earliest embry- 

 onic condition to their adult state and to old age. To complete 

 the series on hand, you should frequently visit the slaughter- 

 houses, where large numbers of our domesticated animals are 

 killed, and also keep in the shed of the Zoological Hall such 

 small species as breed rapidly, to have constantly on hand fresh 

 materials for examination. I would also recommend that you 

 make as many skeletons of embryos as possible, to be preserved 

 in alcohol, that the unossified parts may be studied as well as 



