374 P, HERBERT CARPENTER. 



and nerves. This is figured by Ludwig,^ but Apostolides has 

 failed to find it, just as one often does in the Crinoids unless the 

 sections happen to lie in one particular plane; and on p. 168 he 

 gets rather confused about the aboral ring described by Ludwig. 

 He considers himself to have established " que les pretendus 

 vaisseaux formant le cercle aboral sont dus an tissu conjonctif, 

 dont les granules se colorent tres vivement ;" but he goes on to 

 ask : " Est il (Ludwig) sur que son second cercle aboral n'est pas 

 la serie de bandelettes musculaires qui relient les vesicules de 

 Poll aux intervalles interbrachiaux ? Leur arrangement coincide 

 exactement avec celui du cercle aboral/^ These muscular bands, 

 however, would hardly have the structure represented by Ludwig 

 on fig. 15, viz. a cellular (genital) cord in the centre, with the 

 actual blood space around it, outside which is the perihsemal 

 canal of this portion of the vascular system. 



Passing now to another part of the subject, I would direct 

 attention to the elaborate account of the development of Asterina 

 gibbosa, which has been recently published by Ludwig.- It is 

 accompanied by eight plates, which are filled with figures repre- 

 senting sections of the larva in many different planes, and it 

 throws much light on many obscure points in the development 

 both of Starfishes and of other Echinoderms, as will be seen in 

 the course of the following pages. 



In the face of the controversy relating to the central plexus of 

 the Asterids it is interesting to learn something of its develop- 

 ment and of that of the oral ring, with which Ludwig believes it 

 to be connected in the adult. The latter commences as a cleft in 

 the mesoblast beneath the slight protrusion of the left side of 

 the larval gut, which develops into the fore-gut of the adult. 

 This cleft ends blindly in front, but is continued upwards and 

 backwards into a space which runs close by the water-tube, on its 

 right as seen from the dorsal side. It then bends to enter the 

 mesentery, which separates the cavities of the two peritoneal 

 ca3ca behind the gut, and ends below at the position of the blas- 

 topore. This space, terminating blindly in the mesentery, is the 

 rudiment of the central plexus of the adult. Ludwig says 

 nothing more respecting its later development ; but as the two 

 ends of the mesentery, the one near the water-pore and the other 

 near the anus, are eventually brought close together, it would 

 seem probable that the part of the central plexus which it con- 

 tains is that which joins the aboral ring of the adult, whence 

 (according to Ludwig) the genital vessels arise. 



Now in the Crinoid, the lower end of the mesentery separating 



' 'Zeitschr. f. Wiss. Zool.,' Bd. xxxiv, pi. xv, fig. 16. 

 ' Ibid., Bd. xxxvii, pp. 1-98. 



