204 THE APODID/E PART n 



those of the lateral eyes, their irregularity suggesting 

 their slow disorganisation. 



The very differences then which we find between 

 these sensory organs in Limulus and Apus are in 

 reality more confirmatory of our theory than any 

 exact similarity could possibly be. Similarity could 

 only help to establish the relationship between the 

 two animals. As it is, we have a sufficiently strik- 

 ing likeness with just those differences which are 

 only to be explained by deducing both animals from 

 a common Annelidan ancestor, in the \vay described 

 in this book. 



The alimentary canal has, as already described, the 

 important bend which we refer both in Limulus and 

 in Apus to the bending round of the whole Annelidan 

 body. The chitin-lined cesophageal portion is more 

 highly differentiated than in Apus ; its oral portion is 

 lengthened out posteriorly (or morphologically ante- 

 riorly), showing the same longitudinal folds of its 

 intima as we found in the oesophagus of Apus. Its 

 anterior portion is widened out to form the so-called 

 pro-ventriculus, the chitinous folds of which are so 

 pronounced and differentiated that they probably help 

 in the trituration of food. \Ye here have the homo- 

 logue of the masticatory stomach of the higher Crus- 

 tacea. The posterior end of this projects like a 

 conical crater into the mid-gut, as it does to a much 

 slighter extent in Apus. The mid-gut runs almost to 

 the end of the body, receiving in its course, on each 

 side, two hepatic ducts from the much branched 

 u livers," which fill up a large portion of the cephalo- 



