the MoTjiliology of the Echiaoderms. 115 



ber of the Pentacrinidge, any more than there is of any otner 

 family of Stalked Crinoids, with radiating cavities at its 

 syzygies as described by Prof. Perrier. Even as regards the 

 Comatuloe, which do have more or less appearance of external 

 pores at their syzygies, T cannot accept Prof. Perrier's asser- 

 tion as at all consistent with the facts of the case. I do not 

 deny that pores appear at the syzygies on arms which 

 have been boiled in potash, as was figured by Dr. Carpenter 

 in Antedon rosaceus *j but there is a layer of perisome f out- 

 side the skeleton which is removed by this treatment, so that 

 the pores appear far more distinctly than they do in a dry 

 arm, and still more so than in a fresh or spirit-specimen. 

 This layer of perisome is very well shown in the terminal 

 parts of arms which have been stained with picrocarmine 

 and mounted in dammar ; and the syzygial pores are then 

 seen to be covered by it. The sections which I have made 

 in three planes through the arms of many species of Gomatula 

 have given me every reason to believe that the pores of the 

 skeleton do not open to the exterior through this layer of 

 perisome (which is often much thicker than in Antedon rosaceus) 

 as Prof. Perrier's theory requires ; while I much doubt 

 whether the so-called powerful muscles are anything more 

 tha,n the closely set fibres which form the organic basis of the 

 elevated radiating ridges on the syzygial faces. It is certainly 

 very remarkable that the positions assigned to these muscles 

 by Prof. Perrier are exactly those where the calcareous tissue 

 is densest, on the syzygial faces of fossil arm-joints. I 

 have explained elsewhere % how the organic basis of the 

 pieces of the skeleton becomes m ach more close and compact 

 near those surfaces which are in contact with other joints ; 

 and I believe this to be preeminently the case at the syzygies, 

 though the apposed faces are not so perfectly united as in the 

 case of the basals and radials, for the syzygial unions are 

 severed with great ease. If Prof. Perrier really does believe 

 that water is driven out from pores at the arm -syzygies of 

 Antedon rosaceus, he can prove it in a very simple way. If 

 he will " pith " the creature by removing its chambered organ 

 it will lie still in the water ; and the action of the powerful 

 muscles expelling water from the syzygial pores would surely 

 cause such a disturbance in the surrounding medium as would 



* Phil. Trans. 1866, pi. xxxvi. 



t The " cortical envelope " of Dr. Carpenter. 



X "On the Genus Actinometra, MiilL, with a Morphological Account 

 of a new Species from the Philippine Islands," Trans. Linn. Soc. 1879, 

 2nd ser., Zool. vol. ii. pp. 55-57. 



