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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 ecliinoderms and tlie annelids is almost as justifiable as between the 

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



Fio. 77.— Dorsal view or a spectmen of Comatulella BRAcraoLATA from Austraua, showing tue relative propor- 

 tions OF the arms, hnmtles, centrouorsai. and cirri (reconstructed from the type-speciiiens of Alecto rosea 

 J. UOller). 



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

 structure which can not but ho 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 echiiiotierms aiul the crabs are ultimately 



