Mr.

Mivart adduces this case, chiefly on account of the supposed difficulty of organs, namely the avicularia of the Polyzoa and the pedicellariae of the Echinodermata, which he considers as "essentially similar," having been developed through natural selection in widely distinct divisions of the animal kingdom.

But, as far as structure is concerned, I can see no similarity between tridactyle pedicellariae and avicularia.