112 Dr. P. 11. Carpenter on some Points in 



Comatulce. Thus, then, the only two recent " Encrines " 

 to which Prof. Perrier's very general statement is at all ap- 

 plicable are Pentacrinus and Metacrinus. These two genera 

 have syzygial unions in the stem as well as in the arms ; 

 but the apposed syzygial faces at one of the nodes of the stem 

 are as smooth as they can be, and altogether devoid of any 

 such markings or sculpture as could give rise to the appear- 

 ance of pores along their line of union*. The syzygial unions 

 in the rays and arras, however, are sometimes of a slightly diffe- 

 rent character and present some approach to the condition of 

 the syzygies in the arms of Comatulce. Dr. Carpenter f has 

 described how each syzygial face in the arm oiAntedon rosaceus 

 is " almost flat, except that it presents a series of slightly ele- 

 vated ridges with alternating furrows, which radiate from the 

 opening of the central canal towards the dorsal margin. . . . 

 The two sets of ridges are applied to each other, leaving 

 between them flattened passages that are formed by the corre- 

 spondence of the furrows An examination of decalci- 

 fied specimens shows that the canals are occupied by radial 

 extensions of the ordinary sarcodic basis-substance. The 

 peculiar arrangement of these suggests that, like the ' medul- 

 lary rays ' of an exogenous stem, they may serve to establish 

 a communication between the ' medullary axis ' of this basis- 

 substance which occupies the central canal, and the ' cortical 

 envelope' by which the surface of the segment is invested." 

 The coeliac canal rests in a more or less defined furrow upon 

 the upper or ventral surface of each arm-joint, the so-called 

 ambulacral groove of the skeleton ; and Prof. Perrier tells us X 

 that " au niveau des syzygies, la cavite coeliaque communi- 

 que avec un syst^rae de cavites rayonnant autour du cordon 

 nerveux, entour^es de muscles et qui jouent evidemment un 

 r6le important dans la nutrition de la partie solide des bras." 

 This statement contains much debatable matter. In the 

 first place, one would certainly expect that the contents of 

 these syzygial cavities would be in communication with the 

 axial canal from which they radiate, rather than with the 

 coeliac canal on the ventral surface of the joint ; but in a very 

 large number of Comatulce belonging to the genera Antedon^ 

 Actinometra^ and Promachocrinus the axial canal or radial 



* Zool. Chall. Exp. partxxxii. pp. 4, 5, 13, pis. xxxi., xxxii., xxxvii., 

 xlvii., &c. 



t "Researches on the Structure, Physiology, and Development ol 

 Antedon{Comatula,'L9.mk.) rosaceus. — Parti.," Phil. Trans. 1866, pp.720, 

 721. 



I " R6sum^ de Recherches sur I'organogenie des Comatules,'' Zool, 

 Anzeiger, viii. Jahrg. 1885, no. 194, p. 265. 



