NOTES ON ECHINODERM MORPHOLOGY. 325 



sence in Bathycrinus and Pentacrinus, stating at the 

 same time that in the latter type the cirrus-vessels are given 

 off from enlargements of the peripheral vessels within the 

 nodal joints. This is well shown in fig. 1. Except for the 

 presence of the stem-ligaments (/), this figure would very 

 well represent a horizontal section through the lower part 

 of the chambered organ of a Pentacrinoid with five cirri. 

 The vessels which proceed to these cirri start, as might 

 be expected, from the peripheral chambers, and not from the 

 central vessel ; and the five first cirri are radial in position, 

 just like the cirri on the stem of Peutacrinus. I wish par- 

 ticularly to insist upon this point ; for the primary cirri have 

 sometimes been described as interradial, owing to the one of 

 them being opposite to the anal plate which at first separates 

 two of the radials. This condition, however, is only transitory 

 in Ant. rosacea, all the radials ultimately coming into close 

 lateral union, with a cirrus-socket on the centro-dorsal imme- 

 diately beneath the middle line of each. A good figure showing 

 this point is given by Dr. Carpenter.^ 



I have examined a quantity of larvae from Naples, Torbay, 

 and Arran, all of which have the cirrus-stumps overlying the 

 interbasal sutures, and therefore radial in position. Sars has 

 noticed the same feature in Ant. dentata, and has illustrated 

 it by an excellent figure;^ and I can confirm his observations 

 for the larvae, both of this species and of two other Antedons, 

 one from the "Porcupine,'^ and the other from the "Challenger" 

 dredgings. In all these three larvae the cirri do not appear till 

 the radials have met laterally and the anal plate has been lifted 

 altogether out of the calyx, so that there is no possibility of 

 mistaking their radial position. 



Now let us turn to Perrier's account of their development. 

 He tells us in the first place that the arms are formed by 

 " bourgeons cellulaires partant du sommet " of the cavities of 

 the chambered organ, which unite with similar " bourgeons " 

 from the water-vascular ring. The chambers, however, have 



1 ' Pliil. Trans.; 1866, PI. xli, fig-. 6. 

 * ' Crinoides Vivants., pp. 53 — 66, Taf, viii, fi^'. 11. 

 VOL. XXIV. NEW SER. Y 



