86 PEOCEEDINGS OF THE ACADEMY OF 



Dr. White bas made the ingenious suggestion (See Bost. Proceedings already 

 cited, that these internal tubes and the openings and pores passing into them* 

 may have been for the purpose of drawing in water and injecting it into the pin- 

 nulte, in order to elevate and move them at will, without the agency of a complex 

 muscular system, apparently so inconsistent with the structure of a being so low 

 in the scale of animal life. It is true the unelastic, rigid nature of these little 

 calcareous tubes would seem to be an objection to this view, but this objection 

 would doubtless apply with equal force against the opinion that they were 

 respiratory organs. f Possibly, however, this apparent difficulty may have been 

 obviated by the presence of thin membranaceous sacks within these tubes, sus- 

 ceptible of contraction and expansion to the extent of their internal cavities. 



Our own observations, both of the tj'pical Crinoids and of the Blastoids, 

 have, as already stated, led us to believe that the series of small pieces, prob- 

 ably always originally covering the small central opening seen in imperfect 

 specimens of the latter group, represents the vault, or ventral disc, of the typi- 

 cal Crinoids. We likewise agree with Dr. White and others who reject the 

 opinion that any of the other openings in these fossils were ovarian apertures. 



In all the types of the Blastoidea yet known, these little mesial furrows of the 

 pseudo-ambulacra are distinctly seen leading to the central opening, precisely 

 as the ambulacral furrows on the disc of Comatula lead to the mouth ; aud in 

 the few types we have yet seen with this little central opening covered by mi- 

 nute vault pieces these furrows could be distinctly traced, as already stated, 

 under the covering, into the central opening. Now, from the exact analogy of 

 these furrows to those we have seen passing inward from the arm bases, under 

 the small vault pieces covering the central opening in Cyathocrinus, and as dis- 

 tinct apparently tubular canals, made up of minute interlocking pieces, con- 

 verging upward from the arm openings in Actinocrinus prohoscidialis, to connect 

 with the upper extremity of the convoluted digestive sack, nearly under the 

 middle of the vault, we think the furrows alluded to in the Blastoids may be 

 properly called ambulacral furrows. 



In the true Pentremites, with wide lancet pieces, J the numerous little trans- 

 verse furrows seen passing outward from these mesial longitudinal furrows, 

 and along the pore pieces to the bases of the slender pinnula3, are merely late- 

 ral branches of the central aiubulacral furrow. In a specimen now before us, 

 supposed to be Pentremites elegans, of Lyon and Casseday, the little pinnulae, 

 some of which are more than twice as long as the body, are each composed of 

 a double series of alternately arranged pieces and provided with a distinct 

 longitudinal furrow along the inner side, exactly corresponding to the ambu- 

 lacral furrows in the arms and pinnuke of the typical Crinoids. It is there- 

 fore probable, as suggested by Dr. White, that these furrows, in at least a por- 

 tion of the pinnula;, were provided with receptacles for the ova as in the true 

 Crinoids. 



As widely different as the Blastoids appear to be from the typical Crinoids, 

 it is easy to see that they really possess essentially the same elements of struc- 

 ture ; though in several respects they seem to be more nearly allied to the 

 types composing the section Cystoidea than to the typical Crinoids. In trying 

 to trace out the relations of their several parts to those of the Crinoids proper, 

 ■we have sometimes thought that the lancet pieces might be modified second 

 radials, deeply inserted in the profound sinuses of the first radials. It seems 

 nearly as probable, however, that they may belong to the vault series. In a 

 conversation with Mr. Wachsmuth respecting the structure of these fossils, he 



* We have not seen posi7n'e evidence that the pseudo-ambulacral pores pass into the in- 

 ternal tubes, but we can scarcely doubt that they dc. 



t Currents of water, however, "might have passed into them, by means of the action of 

 cilia. 



X We use the term "lancet pieces," instead of "lanceolate pieces," often applied to these 

 parts, because they are by n" means always lanceolate in form, but often linear, hence i«. 

 would be an awkward expression to describe "the lanceolate pieces" as being "linear in 

 form." 



[April, 



