82 Dr. C. Collingwood on Recurrent Animal Form, 



great weight to external and striking resemblances in form. 

 Under these circumstances, therefore, it can be no waste of time 

 to inquire what connexion exists between the two, and to attempt 

 to point out a cause for agreements of form, in cases where cor- 

 responding agreement in structure is wanting. 



Nature is inexhaustible in resources ; and variety is one of her 

 greatest charms. It is often said that no two things in Nature are 

 alike, and with truth ; for the resemblance, whether in outward 

 form, or in internal organization, always partakes of the character 

 of a near approach, and not of distinct repetition. This is par- 

 ticularly the case with form, which varies more, and is more 

 simple in its variations than structure ; and it is this which con- 

 firms my belief that structure, and not form, is at once the truest 

 basis of Systems of Nature, and the safest criterion in cases of 

 doubt and difficulty. Thus, an Archetypal animal may agree to 

 a certain extent in structure with a vast group of animals, and 

 yet may resemble none of them in outward form. 



It cannot be a matter of surprise, considering the number of 

 such resemblances existing throughout the animal kingdom, that 

 while the study of homologies was making but slow progress, 

 and the true affinities of animals were but little understood, the 

 real nature of many aberrant forms should have been lost sight 

 of in the contemplation of their homomorphic resemblances. 

 Who can wonder if Pliny spoke of the Bat as " the onely bird 

 that suckleth her little ones," in quaint old Holland's phraseo- 

 logy ? What malacologist even can feel surprise that, up to 

 recent times, the Polyzoan Molluscoids were mistaken for Zoo- 

 phytes ? or that Lhuyd, and at one time the illustrious Ellis, 

 should have regarded them both in the light of " remarkable 

 sea-plants," while his predecessor, Baker, had even looked upon 

 them as the production of " salts incorporated with stony 

 matter"? Who can wonder that, before the time of Savigny, 

 the Tunicated Botrylli should have been regarded as Polypes ? 

 that Linnaeus should have placed Teredo among the Annelides ? 

 that, before the Memoire of Dujardin in 1835, the Foraminif era 

 should have been classed with the Cephalopodous Mollusca ? 

 In all these cases (and others might be brought to swell the list), 

 the animals have been raised, or have sunk, from one subkingdom 

 to another. 



But, although they were not always recognized as such, the 

 existence of recurrent forms in Nature could not be overlooked 

 by the framers of systems, inasmuch as they were stumbling- 

 blocks, which almost seemed placed in their path to prevent 

 the natural arrangement of animals from being too easy a task. 

 A too cursory examination has not unfrequently resulted in 

 the false location of an animal, only to be detected, and trium- 

 phantly exposed, by a succeeding zoologist. 



