238 PROCEEDINGS OF THE ACADEMY OP [1879. 



ternal organs of the body for some purpose we entertain no doubt, 

 and the large amount of surface exposed by means of the complex 

 lamellar structure, is strongly suggestive of the principle which 

 prevails in the respiratory apparatus in the animal kingdom gener- 

 ally. We have said that some Actinocrinid&s probably do not 

 possess the pores in the body. It is very significant that it is in 

 these very forms thatwe find columns such as we have just described. 

 Indeed, in general, so far as we have been able to observe, we have 

 found it to be the rule, that those types which have a perforated 

 ventral sac are without pores in the calyx; that those with caly- 

 cine pores do not possess a perforated ventral sac, and that in 

 forms with a flexible vault, or with perforated ventral sac, or with 

 pores in the body walls, the column is generally destitute of any 

 such complex structure, and has only a small, simple aperture. 

 There may be exceptions to this ; in fact we know of some, but 

 these relate exclusively to veiy large species, in which the open- 

 ings in the main body, which we suppose to be respirator}' pas- 

 sages, are inadequate to supply the immense body. The most re- 

 markable examples of this kind are Megistocrinus and Barycrinus. 

 The former, which belongs to the Actinocrinidae, has species with 

 larger bodily capacity than has been discovered in any other genus. 

 It has generally only ten primary arms, and most probably only 

 ten respiratory pores in the body. Barycrinus attains by far the 

 greatest size of the Cyathocrinidee, and the column of this genus 

 like that of Megistocrinus is not only very strong, but its central 

 cavit} r is exceedingly large and complicated. We thus have in 

 these two genera apparently another mode of communication from 

 the outside, which may have been either a cause or an effect of 

 their extreme size. 



All these facts have led us to suppose that the column was in 

 some cases, and perhaps more or less in the Paleocrinoids gener- 

 ally, subservient to respiration. This supposition would not only 

 account for the complicated structure of the column where it ex- 

 its, but furnish a plausible explanation as to how the introduction 

 of water was effected in species in which apparently no other open- 

 ings are present. 



With these observations, which we hope will at least be sug- 

 gestive of some interesting points, and perhaps stimulate more 

 detailed observation, we pass to another matter of considerable 

 importance as bearing upon classification. 



