GENERAL PART. 67 



The development of the tentacles was found in conformity with what is 

 known for Antedon. The primary tentacle remains distinct for some time in 

 the first bifurcation of the arm (plate xxi, figure 7) until it becomes absorbed. 

 Of the triplets of tentacles the distal tentacle is the first to develop. 61 There 

 is no reason to doubt that this will prove the general rule in Comatulids. 



A. H. Clark, in his "Monograph of the existing Crinoids" (pages 313, 314), 

 asserts as an established fact that the infrabasals of Crinoids correspond to 

 the oculars of the Echinoids, and makes the following startling statement 

 respecting the radial water tubes of the Crinoids : 



"In the Crinoids the infrabasals lie at the distal end of the radial water tube, 

 in exactly the same position as the oculars are found in the Echinoids. The water 

 tube of the arms is in reality merely a side branch from the true water tube, which 

 runs around the side of the body from the circumoral ring to the infrabasals, and 

 has no further morphological significance. Though in the later crinoids the water 

 tube leading from the edge of the disk to the infrabasals is insignificant when com- 

 pared with that of the arms, in the earlier forms, in which the calyx was very large 

 and the arms very short, the latter must have been very insignificant when compared 

 with the former. ... It should be emphasized that the water tube grows not 

 only outward into the arm (an offshoot of purely secondary morphological import- 

 ance) but downward into the centrodorsal ; in other words, it eventually comes into 

 its true relations with the infrabasals by growing beyond the radials." 



I must protest against this representation of the development of the radial 

 water tubes and the relations between infrabasals and hydroccel. There is 

 not the slightest indication in the developmental history of the Crinoids that 

 the radial water tubes grow downwards into the calyx to meet the infrabasals, 

 and that the radial water tube of the arms is only a side branch from such a 

 downwardly directed main tube. This is only an imaginary construction 

 arising from the desire to find support for the homology that is maintained 

 to exist between the oculars of Echinoids and the infrabasals of Crinoids 

 an homology for which there is no real support. 



6. THE ENTODERM; HISTOLYSIS. 



The formation of the stomach and intestine in the forms here studied is 

 in perfect accordance with the results obtained in Antedon by Seeliger and 

 his predecessors, so that Antedon probably represents the type of formation 

 of these organs common to all Comatulids (unless there exist Comatulids 

 with a typical pelagic, self-feeding larva). There is only reason to repeat 

 here that Seeliger's view, that the mass of small cells filling the lumen of the 

 entoderm during the metamorphosis from the larva to the Pentacrinoid 

 serves as nourishment for the embryo, is evidently erroneous. 62 As maintained 

 by Bury, and as becomes especially apparent from a comparison with what 



61 The same observations were made by Perrier in his " Memoire sur 1'organisation et le developpement 

 de laComatule de la Mediterranee " (Nouv. Arch. Mus. d'hist. nat. Paris, x, 1889, p. 221, plate 2, fig. 18.) 



62 Seeliger's view is also accepted by MacBride in his "Text-book of Embryology," I, p. 552, 1914. 



