GENERAL PART. 77 



The suggestion would seem to lie at hand that there might perhaps be 

 some relation between the presence of infrabasalia and the position of the 

 first whorl of cirri — that the latter would be interradial in position when 

 infrabasalia were present, and vice versa. This is, however, not the case. 

 The first cirri were found to be radial in position in all cases where their first 

 appearance could be observed, in Compsometra, with infrabasalia, as well as 

 in Isometra and Thaumatometra, without infrabasalia. 



The statement of W. B. Carpenter, that the first cirri of Antedon bifida 

 are interradial in position, is in disagreement with these observations; but 

 Carpenter was in error here (comp. page 29) ; the first cirri are really radial 

 in position in Aiitedon bifida, as they are in all ComatuUds where their first 

 appearance has been observed. This is evidently a general rule in Coma- 

 tulids. A. H. Clark (Monograph of the Existing Crinoids, page 269) sees 

 the reason for the fact that the infrabasals have no influence on the position 

 of the cirri in ComatuUds (and Pentacrinites), while they have such influence 

 in the fossil monocyclic forms, therein, that in the former group " the infra- 

 basals have entirely lost their primitive character as important parts of the 

 body-wall and have become entirely neghgible constituents of the calcareous 

 structure of the organism." I think Clark is right in this explanation. 



^Vhile the arms develop contemporaneously, this is not the case with the 

 cirri. Any definite rule in the succession of their development, however, 

 does not appear to exist. My observations regarding this point are in accord- 

 ance with those of W. B. Carpenter (op. cit., page 733), who found the cirrus 

 "opposite to" the anal plate — ^that is to say, to the right of it — to be gen- 

 erall}^ but not always, the latest to appear. 



Regarding the formation of the cirrus joints, W. B. Carpenter (op. cit., 

 page 733) has come to the conclusion that the new joints are interpolated 

 at the base of the cirrus. A. H. Clark (Monograph of the Existing Crinoids, 

 page 272) states that "the individual ossicles of the cirri are formed as a 

 result of the segmentation and solidification, and simultaneous division of a 

 primitive spicular calcareous investment of the cirri." Both these state- 

 ments are without foundation in reality. It is very easy to see that in the 

 young, developing cirri at the upper edge of the centrodorsal of a Comatulid, 

 the lowermost joints are the largest; on dissolving such developing cirrus, 

 by means of hypochlorite of sodium under the microscope, it is seen that 

 the new joints are added at the end of the cirrus; the same can easily be ascer- 

 tained on the cirri developing in the Pentacrinoid. The terminal joint is the 

 last to form; no intercalation of joints takes place, and no "primitive spicular 

 calcareous investment of the cirri" exists. 



It is worth mentioning that the cirrus joints are formed after another 

 type than that of the columnars or arm-joints. They appear at first as 

 simple, round, fenestrated plates, with no central perforation; this is formed 

 later on by absorption of the central part of the plate (text-figure 9). The 



