MUSEUM OF COMPARATIVE ZOOLOGY. 



EXPLANATION OF THE PLATES. 



a. Blastopore. 



ad. Interambulacrals. 



ad 1 , ad"*, ad 3 , ad 4 , ad 5 . Interambulacrals in sequence. 



am. Oral ambulacrals. 



am 1 , am 2 , am 3 , am 4 , am 5 . Ambulacral rafters in sequence. 



