198 LAKE SUPERIOR. 



In the department of Mollusca, if the above principles are correct, 

 embryology is likely to introduce modifications in our systematic 

 methods, which will entirely overthrow the views entertained at pres- 

 ent respecting their systematical arrangement ; not that we should 

 ever be led to consider Acephala as higher than the Gasteropoda, or 

 these as higher than the Cephalopoda ; but within these classes, taken 

 by themselves, I look for considerable changes, which, when once 

 introduced, might explain why there is apparently so little agree- 

 ment between the geological succession of their types and their 

 systematic arrangement, especially among Gasteropoda. Now it is 

 precisely among these, that I anticipate the greatest changes. It is 

 indeed a remarkable fact, that so many, if not all naked branchiferous 

 Gasteropoda should be provided with a shell in their early age, and 

 lose this protecting envelop as they grow older, which would lead 

 to the conclusion, that among these animals the fact of having a 

 shell indicates a rather lower condition. The comparison of Octo- 

 pus, Loligo, Sepia and Nautilus would lead to similar conclusions. 

 Indeed it is scarcely any longer doubted, that Nautilus has many 

 points of resemblance in common with the Gasteropoda, and from its 

 numerous tentacles (multiplication being always an indication of a 

 lower degree,) must be considered the lowest type among Cephalo- 

 poda ; next we should place the Dibranchiate Cephalopoda, among 

 which the Argonauta, with its external shell, ranks the lowest ; next 

 the naked Octopodidoe, while the Sepiadse with their ten tentacles and 

 internal shell or bone would be the highest in that class. Now if this 

 arrangement be the real order of succession of the Cephalopoda accord- 

 skin of the caterpillar, (in which state the caterpillar is so seldom examined, from fear 

 of disturbing it in its transformation) that under this last skin of the caterpillar, I say, 

 the young butterfly assumes the characters of a Coleopteron. It has then an upper pair of 

 wings, having the character of elytra, and a lower pair of membranous wings. At that 

 time its jaws have not yet assumed the form of a sucker, and are still free, as are also 

 the legs. But these parts, which are easily observed in caterpillaA immersed in diluted 

 alcohol at the very moment when they are casting their last skin, are soon soldered 

 together to form the hard coating of the pupa, and are cast off before the perfect butter- 

 fly comes out. It is, therefore, correct to say, that the structural condition of Coleoptera, 

 in their perfect state, answers to that stage of moulting of Lepidoptera which precedes 

 their perfect development. Coleoptera are, therefore, one stage behind Lepidoptera ; 

 they rank below them ; they are an inferior degree of development of the type of 

 insects. 



