220 



THE APODID^E 



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 



