Revieivs — Wachsmiith tf- Spnnger^s Monograph on Crinoids. 425 



of the forks meet radially, and then enclose the radially placed 

 chambers of the central organ [cli). These, as usual, are disposed 

 around the axial organ [nx), and extensions from all of these pass 

 down into the lumen of the stem. Thus, in Isocrinus the five nerves 

 and vessels of the stem are, as is well known, radial in position, 

 and give off branches to the radially placed cirri, as becomes 

 a dicyclic or pseudoraonocyclic crinoid. 



Admitting the prime importance of the chambered organ and its 

 various extensions, we see that the cirri must follow the course of 

 the axial cords from which they are innervated and nourished ; we 

 may also imagine that the pentameres of a quinquepartite stem 

 were brought from their original alternating arrangement, into 

 vertical lines, by the extensions of the axial cords, between which 

 they therefore lie. On the other hand, there is nothing in the 

 fundamental constitution of a crinoid to prevent the outer angles 

 of the stem, and by consequence its sides, from assuming any 

 position ; and although the angles of the lumen most naturally 

 correspond with the orientations of the axial cord, still secondary 

 formation of stereom may readily cause a change in this respect 

 without upsetting the morphology of the animal. That such 

 secondary formation of stereom does take place is no hypothesis ; 

 it has been described in Antedon by W- B. Carpenter, H. Bury, and 

 others. In fact, the odd thing about that genus is that the very 

 features on which Wachsmuth and Springer relied in their famous 

 prediction that it would be proved dicyclic, are of purely secondary 

 nature. It is to such secondary stereom that the changes in the 

 lumen of the Isocrinus stem may be ascribed. As for Glijptocrinus 

 Fornshelli, it is surprising that no figures are given by Wachsmuth 

 and Springer of a structure that leads to so much discussion, but 

 S. A. Miller's description (1874) is certainly suggestive of a similar 

 explanation. 



For the table given by Wachsmuth and Springer, I propose 

 therefore to substitute the following, in which the statements liable 

 to exception are marked with *. 



From this it appears that the sole constant characters are those 

 presented by the aboral nerve-system, characters which find no place 

 in Wachsmuth and Springer's statement. Thus, I believe, the law 

 first discovered by these eminent palseoutologists can at last be used 



