220 



THE 



PART II 



We have, as has already been pointed out by many 

 authors, the parallel case of the Zoaea, in which the 

 abdomen which is useful to the larva for swimming is 

 developed before the posterior thoracic segments. 



FIG. 49. Asaphos _megistos Hall (after Walcott), showing the well-developed 

 ventral parapodia, and the gradual simplification of the limbs from before back- 

 wards, as in Apus. Cf. Frontispiece ; /, pygidium. 



The Limulus larva, in which the same thing occurs, is 

 on this account called by Packard a Zoaea. 



Having mentioned this habit of rolling up, we may 

 as well here point out that it also forms a link of 

 connection between the Trilobites and the Crustacean- 

 Annelid, it being easily explained as the perfection 



