406 Importance of Habit as a Guide to 



ART. XXXIII. — ON THE IMPORTANCE OF HABIT AS A GUIDE TO 

 ACCURACY IN SYSTEMATICAL ARRANGEMENT, ILLUSTRATED 

 IN THE INSTANCE OF THE SYLVIA PETECHIA OF WILSON, 

 AND ALL SUBSEQUENT WRITERS. By Thomas McCulloch, Jr., of 

 Halifax, Nova Scotia, Corresponding Member of the Wernerian Society of Edin- 

 burgh. 



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Few things, perhaps, have a greater tendency to faciHtate 

 the attainment of any branch of knowledge, than accuracy of 

 arrangement. In numerous instances, however, this is a mat- 

 ter of exceeding difficulty, more especially, in those sciences 

 which have reference to organized objects. There, species 

 belonging to different families, often approximate so closely, 

 that it is almost impossible to ascertain their true position, if 

 directed alone by external development. Unfortunately for 

 the progress of science, this has been too frequently the only 

 guide, and to this circumstance may justly be attributed the 

 numerous and serious mistakes which have been committed, 

 even by very accomplished systematists. Many of these errors, 

 doubtless, might have been avoided by attention to internal 

 structure, and until arrangement, in certain departments of 

 science be based upon this, as well as upon external develop- 

 ment, implicit confidence can never be placed in its conclu- 

 sions. For investigations of this kind, however, there is re- 

 quisite, not only a certain degree of manual dexterity, but also 

 an amount of knowledge both diversified and extensive ; and 

 for the attainment of this, few persons possess either the 

 time or inclination which is necessary. In the absence of 

 these important qualifications, careful attention to habit will 

 be found to form no mean substitute, for habit, in numerous 

 instances, is an infallible index of internal arrangement. It is 

 true, that even in habit, aberrations occur occasionally, where 

 it might be difficult if not impossible to trace correspondence 

 in structure, as in the extraordinary fly-catching propensities 

 of the Picus varius, yet, in general, thorough acquaintance with 

 habit will be found to contribute most materially to accuracy 

 of conclusion. This branch of knowledge is not as""yet suffi- 

 ciently appreciated, though to it, doubtless, we are indebted 



