Revieics — Wachsmuth 8f Springer^ s Monograph on Crinoids. 321 



It is followed in descending order by the suhtentacular canal, the 

 genital canal, and the axial canal." Now the majority of the structures 

 herein mentioned have nothing to do with ambulacra, which are 

 here, as in all Echinoderma, radial extensions from the circum-oral 

 water-vessel, giving off lateral branches, the podia (tentacles of 

 crinoids, tube-feet of sea-urchins). Each ambulacrum may be 

 accompanied by radial extensions of other systems of the body — 

 or it may not. In a crinoid the ambulacra pass to the tips of the 

 arms, so also do the radial extensions of the superficial oral nervous 

 system, the paired cords of the deeper oral nervous system, and 

 the pseudhfBmal canal, none of which structures are mentioned by 

 Wachsmuth and Springer. Those that they do mention are not 

 quite happily introduced, for there are two suhtentacular canals, 

 as well as another extension from the body-cavity, unpaired and 

 lying dorsal to the genital canal. The genital canal contains 

 the genital rachis, which may be an " ovarian tube " or may be 

 of male nature. Finally, the reader must not infer, as he might 

 easily do, from the above-quoted description, that the axial canal 

 with its contained axial cord accompanies the ambulacrum in 

 its tegminal or subtegminal passage towards the mouth ; it separates 

 from it immediately on reaching the walls of the calyx, and while 

 the ambulacrum passes along the ventral surface, the axial cord 

 passes down the dorsal walls to the aborally situate chambered 

 organ. Of course Messrs. Wachsmuth and Springer knew the above 

 facts long before I wrote a line on the crinoids ; but it is just because 

 of their learning and authority that these lapses and ambiguities are 

 so misleading to the student, for whose benefit the chapter is 

 intended. 



To the paragraph defining the term ' perisomic plates ' (foot of 

 p. 36) I turned with interest, because in 1891 these same authors 

 published an important paper on " The Perisomic Plates of the 

 Crinoids," ^ which I have read and reread without discovering what 

 they meant by ' perisomic ' or why they used the word. Moreover, 

 the term has been a rock of offence to others, notably Dr. Arnold 

 Lang, as I ventured to point out in a review - of the section on 

 echinoderms in his valuable text-book. It is doubtful whether we 

 shall be greatly helped by the present definition : " The term 

 perisomic plates is given to all plates which are originally developed 

 from simple, cribriform films of limestone. They comprise the 

 interradials and interaxillaries, the anals, and all ambulacral and 

 interambulacral plates." Of course the definition would "comprise" 

 a good many other plates, such as basals, radials, and orals, but it is 

 still doubtful whether this is the intention of the authors. In some 

 respects the definition approaches that of Wyville Thomson, who 

 first used the term ; but he did not include the radials in his 



^ Proc. Acad. Nat. Sci. Philadelphia, vol. for 1890, pp. 345-392, pis. ix, s. 

 Reviewed in Geol. Mag., Dec. Ill, Vol. Vill, pp. 219-224, May, 1891. 



' " The text-book writer among the echinoderms" : Natural Science, vi, pp. 415- 

 423, June, 1895. 



DECADE IV. VOL. V. XO. VII. 21 



