i84 THE AFODIDJE part ii 



essentially the same place as in Apus, and is known 

 as the sternal plate. If we have given the right 

 explanation of these two points, the bent intestine 

 and the sinewy mass in the bend in Apus, there can 

 hardly be any other explanation to be given of their 

 occurrence in Limulus. Given, then, the derivation of 

 Apus out of a dent Annelid, in the manner described 

 in the first part, it is hardly within the range of pro- 

 bability that Limulus, in which these two essential 

 marks of such a derivation occur, should have had a 

 different origin. These two points of resemblance, 

 occurring together, are, in our opinion, conclusive as 

 to the essential relationship of Limulus to Apus, 

 through their common origin from a bent Annelid. 

 This alone without further positive evidence was 

 sufficient to convince us that Apus and Limulus 

 were at least branches of the same stem. But, as 

 will be seen in the following pages, the whole 

 organisation of Limulus admits of direct com- 

 parison with that of Apus, the very differences 

 between them affording striking confirmation of 

 our theory of their common origin from a bent 

 Annelid. 



With this decisive evidence in favour of our theory 

 we naturally proceeded with considerable confidence 

 in attempting to homologisc the limbs w^hich have 

 hitherto presented the chief difficulty in connecting 

 Apus and Limulus. Before commencing a detailed 

 discussion of the limbs of Limulus, there arc man)' 

 l)oints of resemblance in external organisation which 

 should be mentioned. It will also be useful to 



