ISO 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



and intelligibly explained that can not be explained in any other way. No one of 

 the comparisons is in itself at all conclusive, while in one or two cases a comparison 

 between the echinoderms and the annelids is almost as justifiable as between the 

 echinoderms and crustaceans; but the sum total of the comparisons indicates that 



FIG. "7. DORSAL VIEW OF A SPECIMEN OF COMATULELLA BRACHIOLATA FROM AUSTRALIA, SHOWING THE RELATIVE PROPOR- 

 TIONS OF THE ARMS, PINNULES, CENTRODORSAL AND CIRKI (RECONSTRUCTED FROM THE TYPE-SPECIMENS OF ALECTO ROSEA 

 J. MOLLER). 



there is between the echinoderms and the crustaceans a similarity of fundamental 

 structure which can not but be more than accidental. 



At first sight it may seem unwarranted to suggest, even remotely, a comparison 

 between such highly diverse and relatively recent animals as the echinoderms and 

 the crabs of the present day. Yet in the two groups we have to do with types 

 which are in a way convergent. Both the echinoderms and the crabs are ultimately 



