EMBRYONIC AND LARVAL HISTORIES 67 



adult structure is attained, and it would appear not 

 to have had time to have been profoundly modified in 

 accordance with the larval existence. It would seem, 

 therefore, that we are more likely to meet with actual 



Fig. 14. Mysis stage in the development of Peneus, sp. A 2 , 2nd 

 antenna; Ab. 6, 6th abdominal appendage; T. telson; Th. the 

 biramous thoracic appendages. (After Glaus.) 



adult ancestral types in the late larval or develop- 

 mental stages of fairly closely related animals, which 

 have not had time to be secondarily modified, than in 

 the very early stages of more remotely related forms, 

 although these, in accordance with Von Baer's law, 



52 



