of the Chalk. 179 



Edwards in respect to the Tubulipores*. That writer was enabled, 

 chiefly by this means, to correct the errors of numerous former 

 writers, and to show the true affinities of objects theretofore 

 grouped in most widely different relations. 



If these observations are well-founded, it will follow that at- 

 tention to the nature and structure of polypidoms in general is a 

 matter of much higher importance in determining the true cha- 

 racter and affinities of zoophytes than is generally admitted, and 

 it will appear that a true and careful examination of the combined 

 characters [not any individual points] of structure of polypidoms 

 will afford as safe and important guides in determining the affi- 

 nities, and thereby leading to a just classification, of zoophytes 

 as is afforded by fossil bones to the comparative anatomist in his 

 attempt to vivify the long-departed forms of mammals. No one 

 imbued with the true idea of the Law of Unity, without which 

 science is a mere name, can doubt but that in the one case as in 

 the other, constant relations must exist between one part and 

 another of the entire organization of the recent animal f. 



Nor can this reasoning be in the least degree affected by any 

 theory as to the mode of formation of the polypidom. This will 

 be too obvious to need more than bare allusion. 



The importance of the application of these principles in the 

 investigation of a class of objects like the zoophytes, of which 

 the polyps themselves are so perishable, will be sufficiently evi- 

 dent to the student either of the recent or fossil forms of this 

 most interesting family. 



To apply these principles in the present case. In the poly- 

 pidom of the Ventriculidse, to some of the principal and more 

 striking features in the structure of which our attention has pur- 

 posely been hitherto alone directed, many remarkable characters 

 have been found which distinguish it at once from the polypidom 

 of any zoophyte, recent or fossil, hitherto described. At the very 

 first step of our inquiry into affinities we seem then, at first sight, 

 to be put at fault. And this is true in so far as that it becomes 

 obvious that we can range these bodies among those of no recent 

 genus or even family. But that point alone is something defi- 

 nite. And further, the character of a difference is oftentimes a 

 guide where points of analogy fail. In what respect does the 



* Ann. des Sciences Naturelles, April 18.38, p. 193. 



t Thus the " affinity " named by Dr. Johnston as existing between the 

 polypidoms of Alcyonium and Alcyonidium is only " apparent," being of the 

 merest superficial character. Hence it is that I use, below, Dr. Fane's 

 name of Halodactylus instead of that of Alcyonxdium ; not because I like the 

 prevailing taste for Greek names, but because the two names Alcyonium and 

 Alcyonidium are so nearly alike as almost necessarily to engender erroneous 

 ideas of an affinity between the animals to which they have been applied. 



13* 



