240 



The Chitons have long been a source of difference of opi- 

 nion with naturalists, not only as to their position amongst 

 the Mollusca, but it has been insisted on, that they are apo- 

 cryphal members of that class. The greatest authorities are 

 in collision : M. De Blainville considers that the motive power 

 and other apparatus of the circulation have a rectilinear .dorsal 

 arrangement, similar to that of the Annelida : Cuvier and 

 Lamarck regard them as true Mollusca, ranging with the 

 Patelloid group : Professor Forbes has doubts, and looks on 

 the question as still within the limits of debateable ground, 

 and terms the Chitons malacological " puzzles." Some ob- 

 servers contend, that the reproductive organs, unlike the 

 asymmetrical ones of the Gasteropoda, exhibit a disposition 

 of parities on a medial line, and like M. De Blainville refer 

 them to the Annelida. Milne-Edwards demurs that they are 

 Mollusca, and goes no further than to regard them as an 

 aberrant tribe of Gasteropoda. 



Having dissected many examples of three species, I think 

 that my notes may assist zoologists in coming to soimd con- 

 clusions with respect to natural position. As my investiga- 

 tions have induced a chain of reasoning which has convinced 

 me that the Chitons are true Mollusca of the Patelloid type, 

 it may be as well at once to allude to that part of them which 

 bears upon the objections that have just been stated. 



Though doubts have lately sprung up as to the natural 

 position of these curious animals, they have, until now, been 

 placed by most authors in close connection with the Conchi- 

 fera. If this is right, what then is there extraordinary and 

 unusual in the disposition of the organs of the circulation ? 

 They have nearly the same dorsal rectilinear position as in the 

 Acephala, from which they have long been considered, and I 

 think it will be shown rightly, the point of transition to the 

 Gasteropoda. Why not, therefore, contrast this peculiar 

 arrangement, which is the invariable consequence of the sym- 

 metry of the bivalve animal, with that which obtains in the 

 Chitons from the same cause, and also in others of the Patel- 

 loid tribe that have the same position and a similar parity 

 of their organs? I admit, that the strict Patellae, though 



