MESOSOMA 165 



is founded, in the first instance, upon the mutual 

 topographical proximity of the respiratory appar- 

 atus, and of the terminal portion of the genital 

 apparatus in the scorpion group and in Limulus 

 the King Crab, and the relations of these organs 

 to the segments of the mesosoma. 



It is not easy to deal with this comparison 

 in a satisfactory manner. It seems to be some- 

 what gratuitous and to proceed from a fallacious 

 assumption of community of regional differentia- 

 tion. We have seen in several instances that 

 identity of structure and function may go for 

 nothing in determining homology, and that the 

 same identity has no relation to topography. If 

 one chooses to compare the respiratory region 

 of the scorpion or of Limulus with that of 

 Ammocoetes, and to dub it mesosoma in both 

 cases, all sorts of curious sequences will be 

 encountered. Without a preconceived bias, such 

 as Dr Gaskell does not conceal, namely, in 

 respect of his ideas upon dominance and brain- 

 power, one would not consider the two regions 

 comparable morphologically. It is a very good 

 thing to have a guiding idea in morphology and 

 to follow it out, but at the best it can only lead 

 to a subjective conclusion. There is no necessity 

 to confound such a conclusion with the truth, 

 and this is all we can ask, since the reconcilia- 

 tion of the truth with one's individual views 



is not a matter which can be settled within a 



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