36 SMITHSONIAN INSTITUTION 



connect, must necessarily be the same as that of the lobes of the chambered 

 organ, the primary axial cords, and the proximal plates of the base, namely, 

 interradial in monocyclic and radial in dicyclic crinoids ; and the orientation of 

 the original pentameres of the stem must alternate with them. It would be 

 expected that these peripheral vessels, whose branches follow the suture lines 

 of the original pentameres, would lie at the corners of the central opening 

 formed by the junction of the pentameres, and that this central canal when 

 angular or petalous would have the same definite orientation as the cirri, and 

 be uniformly radial in dicyclic forms. But in fact we find that this is not 

 always the case with the central canal formed by the hard parts of the stem as 

 we find it in Recent crinoids treated with potash, and in fossil forms. In most 

 species of Isocrinus and Metacrinus the canal, angular in the newer parts of 

 the stem, is distinctly interradial, while the peripheral vessels are radial; and in 

 the majority of the Flexibilia, so far as observed, the stem lumen as we see it is 

 interradial. 



In studying the question in the Recent crinoids, it is found that while the 

 peripheral vessels in the stem form a pentagon whose outer angles coincide 

 with the cirri and the vertical sutures, they do not fill the space within the stem 

 lumen or central opening within the calcareous walls of the stem, but are sur- 

 rounded by a fibrillar envelope of perishable substance which is destroyed by 

 potash dissection; the same thing would happen during fossilization. These 

 peripheral canals are relatively minute, and do not occupy more than half of 

 the central opening surrounded by the calcareous substance of the stem (see 

 P. H. Carpenter, Stalked Crinoids, pi. 24, figs. 1-4). Hence they can have 

 nothing to do with determining the shape or orientation of that opening. 

 Therefore it must be said that owing to secondary growth, or for some un- 

 known reason, the form and orientation of the stem lumen are independent of 

 the peripheral canals, and may or may not coincide with them. And the lumen 

 may also have a shape totally inconsistent with the existence of any definite 

 connection between them, as for instance in Cupressocrinus, Schultsicrinus, 

 Myrtillocrinus, Arachnocrinus, etc., in which the stem canal may be three or 

 four sided. 



The foregoing facts confirm the view expressed by Bather in the Lankes- 

 ter Zoology, pt. 3, p. 106, that with regard to the orientation of the stem canal 

 the law of Wachsmuth and Springer is empyrical and subject to exceptions. 

 With the facts now known it would seem to apply chiefly to those forms, 

 whether monocyclic or dicyclic, in which the plates of the lowest ring are equal, 

 and even in those there are some exceptions. In view of the exceptions and 

 irregularities thus observed, and of the variable shape of the stem canal in dif- 

 ferent genera and sometimes even within the same genus, as in Cupressocrinus, 

 the orientation of the stem lumen may be regarded as a matter of minor impor- 

 tance in the morphology of the crinoids. 



