414 THE VOYAGE OF H.M.S. CHALLENGER. 



Loven lias recently pointed out the singularly Crinoidal appearance of the calycinal 

 system of a Triassic Urchin, Tiarechinus princeps, Laube.^ " The relative magnitude of 

 the entire system, the prominent share it takes among the constituents of the skeleton, 

 the forms and proportions of its parts, are such as forcibly to recall the calyx of some 

 Palseocriuoid, and to justify a desire to turn the Echinoid upside down and to see the 



calycinal system in its imaginary original position, when it 

 formed a part of some remote ancestral type. In this respect 

 the resemblance becomes still more striking." 



Let us compare Lov^n's figure (fig. 21) with that of the 

 Blastoid (fig. 20). Each has relatively large basals (B) ; l)ut 

 the radials of the Pentremite (R) are small in Tiarechinus, 

 their limbs being replaced by the two lateral plates of the 

 interradius (^) which enclose the ambulacrum. In Tiare- 

 „„,„.,. , , c/;m7f.f, just as in the Blastoid, however, the ambulacrum ends 



Fig. 21. — Tiarechimis prmceps, Laube, ■' ' 



iTTi^'^McaTsy^stertfthrcalyx o?°a ^gaiust the body of the Corresponding radial ; and its nerve, 

 ^^^^^: .Zr"ls^^:)''V'tJ^\\ lyiiig beneath the ambulacral plates as in recent Echini, 

 ittrtiakftrS''^*" ' '■""™' ^'o^^ld be in a position where it could be directly continuous 



with an axial cord situated within the radial or on its inner 

 face, if only Tiarechinus were a Crinoid instead of an Urchin. I would not, of course, 

 be understood as saying that Tiarechinus had a central capsule and axial cords pro- 

 ceeding from it. My only object has been to jaoiut out that Loven's happy comparison 

 of this curious type with an inverted Crinoid alFects other systems of organs besides that 

 of the calycular plates. At the same time, considering the number of Asterids which 

 have a calyx of relatively large plates, and the fact that there is a continuous nerve 

 sheath on the dorsal surface, I think it not improbable that indications of a central 

 capsule and axial cords may eventually be discovered in the Echinozoa. 



It remains now to notice the observations of Dr. Jickeli, which, though only published 

 recently, are nearly four years old.^ Like Marshall he has made an elaborate series of 

 experiments in extension and confirmation of those originally described by Dr. Carpenter, 

 whose views respecting the nervous nature of the central capsule and axial cords he 

 adopts unreservedly. He further believes that the fibrillar bundles uniting the cirrus- 

 joints and those forming the dorsal and interarticular ligaments (as they are described 

 above) in the arms (PI. LXIL, Id, li) are muscular in function, though differing in many 

 points from the fibres which have hitherto been exclusively described as muscles 

 (PI. LXIL, m); for when the axial cord of a detached cirrus is stimulated " so krlimmt 

 sich derselbe auf das Heftigste zusammen und gerath selbst in Tetanus." ^ 



* On Pourtalesia, loc. cit, p. 65. 



2 Vorlauflge Mittheilungen iiber den Bau der Echinodermen, ], Ueber das Nervensystem und die Sinnesorgane 

 der Comatula mediterranea, Zool. Anzeiger, vii. Jahrg., pp. 346-349 and 366-370, 1884. 

 2 Zool. Anxeiger, vol. vii., 1884, p. 348. 



