On Aquatic Carnivorous Coleopiera or Dytiscidce. '96!)' 



that the Carabidoe in whole or part are modified Dytiscidae. Indeed Herr Kolbe's 

 theory and classification are so evidently based on a false premise that it is not, 

 I think, necessary to point out in detail their unsatisfactory character. 



The close approximation existing between the Carabidteand Dytiscidse does not. 

 in my opinion, at all bear out the theory that it is the result of descent from a 

 common ancestor. It is quite certain if the approximation is due to heredity, 

 that the most primitive forms of the two families should bear a resemblance to 

 one another, not only in one special point but more or less in other points ; for 

 it is clear that as we go back in the genealogy and approach the common ancestor 

 so must the descendants become alike in more than one point : there must be 

 as it were an approximation on all points, not only on some special point. This 

 is not, however, what we find to be actually the case : on the contrary, if we take 

 the most primitive forms, such as Pelobius, Amphizoa, Methles, Hydrovatus, 

 Suphis, and compare them together we are struck with the fact that we have before 

 us some of the most dissimilar of the Dytiscidse. The same fact is true of those 

 CarabidaR to which the Dytiscidse approximate ; Trachypachini, Pseudomorphini, 

 Scaritini, and Cyclosomus are in fact about as dissimilar Carabidse as could be 

 selected from the whole of that enormous family. 



If we approach this interesting question from another point of view, that of the 

 structure of any one part, we are brought to a similar conclusion : for instance, if the 

 highly developed prosternal process of the Dytiscidse and of certain Carabidse is an 

 indication of genetic community, then it is clear that it is one of the most ancient 

 and fixed features of the Dytiscidse, and as it is a great advantage to its aquatic 

 possessors, we ought to find it absolutely constant amongst them ; but this is not 

 the case, the prosternal process remains comparatively rudimentary in several 

 widely separated Dytiscidse (Vatellini, Tyndallhydrus, Andex) ; and it is clear that 

 if the Dytiscidse and Cyclosomus possess this structure in common because their 

 primitive ancestor possessed it, then Vatellini, &c., must have separated from this 

 common Dytiscid-Carabid ancestral stock before this part was developed ; a con- 

 clusion which is absurd ; or that the Vatellini have lost by degeneration a character 

 which they formerly possessed, and whose possession was advantageous to them ; 

 a conclusion which there is not the least reason for believing, and of whose truth 

 it would require very weighty evidence to convince us : and which is in opposition 

 to the law of survival of the fittest. It is in fact quite clear that the highly 

 developed prosternal process in Cyclosomus and the Dytiscidse is not the result of 

 genetic community, but has been separately acquired. As regards Pelobius which 

 is truly a " connecting link " between the Carabidse and I dytiscidse, there is not 

 the least reason too for supposing that it is ancestral to any Dytiscidse or any 

 Carabidse, and there do not appear to me to be any grounds for supposing that 

 the Carabidse are the ancestors of the Dytiscid^, or the Dytiscidse of the Carabidaj. 

 If however, under the term " Carabidse " we include not only the known existin»- 



