MALACOZOA. 7 



the objects of the Conchologist's iuvestigfition as they were 

 before their somewhat diverse nature was ascertained.* The 

 Tunicata and Br^^ozoa, on the contrary, have never received much 

 attention from Conchologists, the first because they could only 

 be preserved in spirits and thus were inaccessible to most 

 students, the last because their microscopic size and their aggre- 

 gation into encrusting colonies caused them at first to be con- 

 sidered of much simpler organization than modern investigation 

 has proven to be the case. 



The classes of the malacozoa may be tabulated as follows : 







MALACOZOA. 



J. ^Mi 



OLLUSCA, 







a. . 



Encephala. 





Class 1. 



Cephalopoda. 





Class 2. 



Pteropoda. 





Class 3. 



Gastropoda. 





Class 4. 



Scaphopoda. 





h. Acephala. 





Class 5. 



Pelecypoda. 



B. MOLLUSCOIDA. 



Class 1. Brachiopoda. 

 Class 2. Tunicata. 

 Class 3. Bryozoa. 



The systematic arrangement of natural objects, says Wood- 

 ward, ought not to be guided by convenience, nor framed merelj" 

 for the purposes of easy remembrance and communication. The 

 true method must be suggested by the objects themselves, by 

 their qualities and relations ; — it may not be easy to learn, it 

 may require perpetual modification and adjustment — but inas- 

 much as it represents the existing state of knowledge, it will aid 

 in the understanding of the subject, whereas a dead and arbitrary 

 arrangement is a perpetual bar to advancement, containing in 

 itself no principle of progression. 



* The acceptance of the view originally propounded by Steenstrup and 

 so ably urged by Professor Morse, respecting the affinities of the brach- 

 iopods with the worms (Proc. Bost. Soc, Nat. Hist., 1873), does not 

 to my mind weaken the opinion I have always held as to their affinities 

 with the Polyzoa (Bryozoa), on the one hand, and with the higher mol- 

 lusca on the other." — Huxley, Anat. of Invert. An., 468. 



