218 FOURTH REPORT — 1834. 



Rhgiie Animal, also published in the year 1829, does not differ 

 materially from that in the first. There are simply two additional 

 orders in the class Gasteropoda ; one, named TuhuUhranches, 

 including the genera Vermetus, Magilus, and Siliquaria ; the 

 other, that of H^teropodes, adopted from Lamarck. 



From a review of the above systems, which have been briefly 

 sketched out in the preceding pages, it would seem that even the 

 primary groups in this branch of the animal kingdom are not 

 all determined with certainty. At the same time it is probable 

 that whatever alterations may be suggested by further researches, 

 they will not greatly interfere with those established by Cuvier, 

 and adopted with more or less modification by the generality of 

 naturalists. What we most vrant is a more exact determination 

 of their relative values. The ,Ci)'ripeda, however, probably do 

 not belong to the Molluscous type at all, as appears from re- 

 searches to be further alluded to hereafter. There is also great 

 uncertainty with respect to the exact situation, as well as limits, 

 of some of Cuvier's smaller groups, such, for instance, as his 

 Gasterojjoda Cyclohranchiaund Scutibratic/iia, of which Latreille 

 makes a distinct class. The genera Capiilus, Crepidula, Navi- 

 cella, and Calyptrcea, which are by most authors referred to the 

 Scutihranchia, and which Cuvier himself placed in that order in 

 the first edition of the R^gne Animal , in the second hehas referred 

 to the Pectinihranchia, stating it as his opinion that they come 

 near the Trochidce. Indeed, in none of the classes has the chain 

 of affinities been hitherto worked out with any degree of cer- 

 tainty. We still require further anatomical investigations, both 

 in order to determine with more exactness the actvial structure of 

 many entire families, and to learn the relative importance of those 

 organs from which naturalists have drawn their principal charac- 

 ters. Where we find the organs of motion, circulation, and re- 

 spiration, as well as the mode of I'eproduction, all varying to the 

 degree they do in these animals, it is clear that we must proceed 

 with great caution in endeavouring to ascertain the respective 

 degrees in which they are entitled to our confidence. 



Before, however, quitting this division of the subject, it will be 

 right to notice several important memoirs which have appeared 

 of late years, connected with the structure and affinities of some 

 of the above classes in particular. 



1. Cephalopoda. — All, except Lamarck, allow that this class 

 stands at the head of the Inarticulate Invertehrata, although it 

 is not decided to which of the Vertebrate classes it shows most 

 affinity. Cuvier, who was the first to make us acquainted with 

 the anatomical details of these animals, and who has particu- 

 larly noticed the striking development of some parts of their 

 organization, nevertheless does not allow that they conduct to 



