28 



be sufficiently evident that the important and satisfactory results 

 already arrived at as to the structure of the polypidom of the 

 Ventriculidse never could have been attained, and without it they 

 never can be verified. 



I cannot give a more conclusive or satisfactory illustration of 

 what may be done towards attaining a correct knowledge and 

 just classification of the polyps themselves by a careful inves- 

 tigation of the true nature and structure of polypidoms super- 

 ficially very different, than by reference to the labours of Milne 

 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 01 this 

 most interesting family. 



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

 pidom of the Ventriculida3, to some of the principal and more 

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



* Ann. des Sciences Naturelles, April 1838, p. 193. 



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

 polypidoms of Alcyonlum and /llcyonidium is only " apparent," being of the 

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

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

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

 Alcyomdium are so nearly alike as almost necessarily to engender erroneous 

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



