THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY, 



[THIRD SERIES.] 

 No. 32. AUGUST 1860. 



XIV. — On Recurrent Animal Form, and its Significance in Syste- 

 matic Zoology. By Cuthbert Collingwood, M.B., F.L.S., 

 &c* 



No one conversant with Zoology can have failed to remark the 

 fact of the recurrence of similar forms in different groups of the 

 animal series. Not only do species of one family resemble species 

 of an allied family, but group with group, order with order, and 

 even class with class, and subkingdom with subkingdom, can pro- 

 duce instances of the most striking homomorphism. The resem- 

 blances to which I allude are those of external form, unaccom- 

 panied by homologies of internal structure; nevertheless I 

 imagine that this peculiarity, instead of entirely destroying its 

 interest, and rendering it valueless, as some have appeared to 

 consider, only places the subject in a different category of scien- 

 tific facts, and invests it with a value peculiar to itself. In the 

 history of classification it has always naturally happened that ex- 

 ternal form, rather than internal structure, has been the main- 

 spring of systems ; the knowledge of structural homologies has 

 been painfully accumulated, and the systems built upon the 

 characters presented by external form have from time to time 

 been corrected by increasing knowledge of structure, till in 

 these days zoologists have agreed that structure, and not form, 

 should be the basis upon which systems should be framed with 

 the greatest claim to accordance with Nature. Nevertheless 

 systems founded upon homologies are liable to be interfered with, 

 and their symmetry affected by encroachments of form ; so that 

 eminent zoologists differ as to the position of animals, even in the 

 present advanced state of zoology, owing to the fact that, while 

 one regards homologies of structure as paramount, another allows 



* Communicated by the Author, having bee a read before the British 

 Association at its Meeting at Oxford (I860). 



Ann. § Mag. N. Hist. Ser.3. Vol, vi. 6 



