. Bulletin - United States National Museum. Science. 128 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. But in most primitive echinoderms, such as the stalked cimoids, blastoids, and cystideans, a permanent attachment by an elongated cephalic stalk, in typical cirriped fashion, was the almost invariable rule, and no doubt represented the primitive condition for the whole class. When an echinoderm docs become free it acquires only a very limited power of locomotion and of coordinated movement. Its characteristic lack of efficiency in this respect is due not so much to its simple or primitive struc
. Bulletin - United States National Museum. Science. 128 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. But in most primitive echinoderms, such as the stalked cimoids, blastoids, and cystideans, a permanent attachment by an elongated cephalic stalk, in typical cirriped fashion, was the almost invariable rule, and no doubt represented the primitive condition for the whole class. When an echinoderm docs become free it acquires only a very limited power of locomotion and of coordinated movement. Its characteristic lack of efficiency in this respect is due not so much to its simple or primitive structure as to the fact that its freedom was gained at a lato period in the phylogeny of a very ancient group in which sessile inaction was the prevailing condition. It is often assumed that a sessUe or parasitic mode of life is the initial cause of degeneration. The various anatomical peculiarities common to the cope- pods, cirripeds, and acraniates do not bear out this conclusion. The fact that in these diverse subphyla we see the same shifting of cephalic appendages to the hfemal side, the same cephalic outgrowths, and the same degeneration of the neu- romuscular organs, indicates that there are certain initiixl defects or peculiarities of germinal material common to the whole group, and that these are the underl^ving cause of defective organization, the defec- tive organization being in every case of such a nature that a sessile or parasitic or vegetative mode of life is the only one ; Professor Patten doubts very much whether it will ever be possible to make precise or detailed comparisons of any value between relatively modern types of arthropods, like the decapods and insects, and the echinoderms. My attention was directed toward a comparison of the adults of the two groups on account of the liigh degree of specialization of the echinoderm lai-vsc, and the difficulty of bringing into satisfactory correlation the data offered by the very diverse young of the dif
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