68 CALAMOCKINUS DIOMEDiE. 



The difficulties introduced by Love*n and by myself* in our both at- 

 tempting in a different way to find the homolognes of the plates of the 

 Crinoids, one from the monocyclic and the other from the dicyclic type, 

 have been happily solved h) Carpenter,! who pointed out that the true 

 homologies consisted in always comparing plates radially or interradially 

 situated; that the first basals of Lovon's terminology were radials, the 

 second interradials ; and that naturally the genitals of Echini, being in- 

 terradial, could not be homologous to the first parabasals, but must be 

 homologous to the second parabasals. 



Carpenter has clearly shown the confusion which arose in the nomen- 

 clature of the basis and parabasals from the supposition of Midler that the 

 basals must always rest on the uppermost stem segment. 



It thus becomes clear that the interradially placed basals of monocj'clic 

 Crinoids, the genitals of Echini, the first ring of interradial (referring to 

 their position only) plates in the young Starfishes and the young Ophiurans 

 are homologous. 



We have a central plate in the embryo Starfish, Ophiuran, Sea-urchin, 



* In the earlier attempts to homologize the apical system of Echini with the Crinoids, both Loven 

 and I committed the same mistake which ^Iuller made in looking upon the plates occupying the ring 

 next to the stem as the basis. 



Carpenter did not seem to realize that in 1884 there was but little uniformity in the nomenclature 

 of the plates of Crinoids ; and the very fact that in Comatula the basals undergo considerable meta- 

 morphosis to form the rosette went far to convince me that such a coalescence of the basals was not 

 unnatural. 



Zitt-I speaks of the central plate of Marsupites and of Agassizocrinus (which is within the ring of 

 infrabasals) as the homologue of the centrodorsal of the young Comatula and the odd central plate of 

 the apical system of Echini. He also suggests that the centrodorsal plate of Apiocriuus, with its five 

 radially placed edges, on the top of the upper stem joint, is a coalesced infrabasal. 



Johannes Walther says (Untersuchungen iiber deu Bau der Crinoiden. Palreontographica, XXXII., 

 1SS6, p. 156) that under certain illumination the centrodorsal shows traces of radial sutures : " in die 

 einspringenden Winkel lenken die 5 Basalia ein." 



We cannot follow Walther in his estimate of the value of the vertical sliding of a morphological 

 plane from a lower to a higher horizon, in order to account for the formation of the dicyclic bases of 

 Crinoids from the monocyclic. The oldest known Crinoids have a dicyclic basis, and there is nothing 

 in the development of Antedon to show from the observations of Bury, who discovered the presence of 

 embryonic infrabasals. that the infrabasals are not resorbed ; while, on the contrary, the monocyclic 

 Crinoids are of later origin than the dicyclic. and this is supported by palseontological evidence. What 

 he says of the impossibility of the formation of the infrabasals from the upper stem joint need not be 

 discussed, in view of the facts here presented of the nature of the pentagonally lobed body found on 

 the top of the upper stem joint in Calamocrinus. 



All attempts at homologies based upon the comparison of structural features of one class of the 

 animal kingdom with those of another can only tend to increase the existing confusion, and 

 Walther's attempt to determine the position of his imaginary axis from the position of the anal open- 

 ing and the course of the alimentary canal is at variance with all our present ideas of Echinoderm 

 morphology. 



f On the Oral and Apical Systems of Echinoderms, Quart. Journ. Micr. Sci.. XVIII., 1878, p. 351. 



