MOLLUSCOUS ANIMALS. 321 



these remains a subject of discussion among naturalists of the present 

 day. 1. Linneeus, in conformity with views prevailing in his time, 

 placed the barnacles and acorn shells among the Mollusca, in his 

 division Multivalve shells : even Cuvier allowed them, though as a 

 separate order, to retain this connexion, and if La Marck made them a 

 class, the gain was not great as they were but a class of Invertebrate 

 animals — a confused ill-defined assemblage, in which the grand dis- 

 tinctions of Articulate, Molluscous and Radiate animals are neglected. 

 Few modern naturalists hesitate about placing Cirrphopoda, the barna- 

 cles, &c., as a division of the class Crustacea among Articulate 

 animals. Their belonging to the iVrticulate sub-kingdom is no longer 

 questionable. 



2. There is a group of minute animals, in outward appearance 

 much resembling Hydroid polypes, of which they were considered as a 

 section, which, on a carefu! examination of their structure, are found 

 to constitute a low form of Molluscous animals, and under the name 

 of Polyzoa, or Bryozoa, are accounted a class or sub-class of Mollusca. 

 "We may have to consider as we proceed, their precise position and 

 rank, but it is no longer disputed that they belong to the series which 

 forms our present subject. 



3. A question has of late been raised, and is still in controversj'- 

 among the most eminent living naturalists, whether the great series of 

 animals which fall under the definition I have proposed, and which 

 are generally spoken of as Mollusca, should continue to be regarded 

 as one sub-kingdom or branch, or ought to be divided into two 

 portions, each claiming that rank. It is maixitained by some that 

 such a division is rendered necessary by sufficiently important dis- 

 tinctions, and it is proposed to retain the name Mollusca for the 

 higher division, and to call the other MoUuscoida. 



It must, of course, be remembered that in every great division we 

 have to expect, with uniformity of general structural plan, both 

 various adaptations to different modes of life, and all possible grades 

 of development^from the highest to the lowest which are reconcileable 

 to the common plan. So long then as we can trace the common plan 

 we ought to be so far from separating its lower from its higher grades 

 that the extent of variations of this kind should assist us the better to 

 appreciate the importance of the general characters, and impress the 

 common relationship more strongly on our minds. A Polyzoan and 

 a Gasteropod, may be pretty widely separated, but I confess I cannot 



