il8 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



of the Ordovician crinoids at Kirkfield, Ontario, seems to indicate 

 such a condition of affairs. Here we have the bases of the crinoid 

 columns cemented to an old, hardened and eroded sea bottom. It 

 is obvious that this area had been emerged and upon its sinking the 

 crinoids came in with the gradually advancing sea. The lack of 

 sediment, and the fact that the crinoids are cemented directly to this 

 eroded surface, indicate that the crinoids lived there very shortly 

 after submergence. Submergence in such cases is admittedly a 

 gradual process and of necessity these crinoids must have lived in 

 quite shallow water. It is evident that even moderate wave activity 

 would serve to loosen these crinoids from their points of attachment. 



Effect of forcible dekichment on the organisms. — It may easily be 

 seen that if the majority of the Pelmatozoa were forcibly detached 

 at different times in their ontogeny, and were they to live under 

 such conditions that they might at any time be torn from the bottom, 

 no complicated organs for the purpose of permanent fixation would 

 tend to be evolved. Rather, the exigencies of such a life would tend 

 to perfect the organism in the wa}" of acquiring structures for tem- 

 porary attachment, or to cause them totally to abandon all attempts 

 toward permanent fixation. Here, with the exception of those 

 Cystidea where fixation had not yet become wholly effective, we 

 probably see the prime cause for the inception of detached conditions 

 among the Pelmatozoa. Generahzmg, one may say with a consider- 

 able degree of certaint}^ that a free-swimming or pedunculate form 

 of existence among the Crinoidea is induced by a comparatively 

 shallow water habitat. Although free-swimming crinoids are found 

 at great depths, it is only reasonable to suppose that they have 

 secondarily sought the abyssal zone. The greater number of free- 

 swimming crinoids are to be found either in shallow water or in 

 regions largely affected by strong oceanic currents. 



Having to a greater or less extent forcibly been compelled to as- 

 sume a semidetached existence generation after generation, it is but 

 natural that in certain lines a tendency would be induced toward the 

 more perfect acquisition of such a mode of life as being of consider- 

 able benefit to the animals. Such a tendency is apt to make itself 

 most evident among the terminal members of various genetic lines. 

 Here, probably owing to the impaired force of the tendency toward 

 fixation, complete detachment from the column may become effective. 

 This freedom of the animal is further made possible b}^ the possession 

 of structures that are sufficiently perfected as organs of locomotion 

 to enable the echinoderm to maintain a truly eleutherozoic existence. 



Advantages of a detacJied existence. — The ability of a crmoid to move 

 from place to place is obviously of great advantage. Irrespective 

 of the movement of the cihated larvae, selective migration of the 

 adults largely makes for the welfare of the Crmoidea. Grantmg that 



