68 ME. p. H. CAEPEXTER ON THE GENUS ACTINOMETEA. 



dorsal cirrlii, he described this species as having a cohimu of three segments, and gave 

 a sectional ligure in support of his statements ', which shows three segments below the 

 circlet of fii'st radials, each bearing a row of cirrhi. It is doubtful how far this figure can 

 be relied on as accurate, though I have occasionally met with somewhat similar appear- 

 ances myself. Goldfuss, like Miller, was unacquainted with the remarkable condition 

 of the basals in this type ; and as the " pelvis " described by IMillor in Comatula was 

 rightly regarded by him as representing a part of the stem of I'eiilao'iiins, he was led 

 to believe in the absence of basals in Com. mediterranea, though he found them in the 

 Com. midtiradiata {Comaster), in which he described the rudimentary column as con- 

 sisting of only a single segment. Mi'iUer was led, by his comparison of the component 

 pieces of the calyx of Comatula with those of the calyx of Pentacrinus asteria [Caput- 

 medusce), to recognize the very close general correspondence between them ; and he 

 pointed out - that the presence of cirrhi at tlie upper end of the stem of the Penta- 

 crinoid larva on the one hand, and on the centrodorsal plate bearing the first radials 

 of the young Comatula on the other, indicate that the latter is comparable to the stem 

 of ]?entacrinus, which bears the cirrhi in verticils separated by longer or shorter in- 

 tervals. This view of Miiller's was pretty generally recognized as the true one, and it 

 was adopted and greatly strengthened by Wyvillc Thomson and Dr. Carpenter, who 

 came to precisely the same conclusions upon developmental grounds. The former 

 defined it as representing a " coalesced series of the nodal stem-joints in the stalked 

 Crinoids," namely, of those joints which bear whorls of cirrhi, so that " the centro- 

 dorsal plate with its dorsal cirrhi in Antedon is the homologue of the stem with its 

 cirrhi in the stalked Crinoids." Ludwig ^ also, while referring to the development of 

 the centrodorsal as the enlarged uppermost stem-segment, speaks of it as " ein zusam- 

 mengcdrtingtcr, obercr Stengelabschnitt, in wclchem das verkalktc Gcwebc kcine Sonde- 

 rung in untcreinaudergelegene Glieder crfahrcn hat." 



(§ 47) The first rudiment of the stem of the Pcntacrinoid larva as described by 

 Wyville Thomson ' consists of a series of delicate calcareous rings forming a curved 

 line, which passes backwards from beneath the centre of the lower ring of plates, the 

 embryonic basals. Within each of these is formed a hollow sheaf of parallel calcareous 

 rods, united together by short anastomosing lateral branches ; the upper one of these, on 

 which tlie lower edges of the basal plates rest, soon becomes considerably wider and 

 thicker than the rest. " During the earlier stages of the growth of the Pcntacrinoid it 

 is simply a circular band of the ordinary calcified areolar tissue, enclosing a sheaf of the 

 peculiar fasciculated tissue of the stem, gradually enlarging, with a central aperture con- 

 tinvious with the bore of the tube-like stem-joints." 



This ring is sul)sequently developed into the permanent centrodorsal piece ; but the rudi- 

 ments of the first dorsal cirrhi do not appear around its lower contour until very much 

 later. New rings are developed immediately beneath it, until there are fifteen or sixteen 



' Pctref. German, p. 202. - Bau des l\ntucrinus, p. 10. 



' " Zur Anatomic des Bhizocrinus lofotensis, "Zeitschr. fiir wisa. Zool. Bd. sxix. p. 127. 



* " On the Embryogeny of Antedon rosacetts (Linck) (^ComaUtla rosacea of Lamarck)," Phil. Trans. 1865, pp. 536', 

 537. 



