OUR KNOWLEDGE OF NEW ZEALAND HOLOTHURIANS. Ill 



wheels appear to differ both from those of C. dunedinensis, as described by- 

 Den dy *, and also from those of C. pisanii, as described by Liidwig f. 



In C. 2)'isanli a plug is developed from the original six-rayed cross, which 

 grows up and fills the round hole left between the spokes on the outer face of 

 the wheel. In C. dunedinensis this plug is not developed, and the round hole 

 on the outer face is left open. 



In C. gigas, on the other hand, the six spokes on the outer face themselves 

 unite completely in the middle, and form a round papilla without any 

 perforation. A plug is not developed and the papilla in the centre of the 

 outer face of the wheel is thus formed quite difPerently from that of 

 C. pisanii. The development of these spicules (figs. 11^, 11/) appears to 

 take place as in C. dunedinensis, and the young forms have a round hole 

 in the middle of the outer face, as in that species. 



A single four-rayed wheel (fig. 11 </) was found ; this is a point of some 

 interest, as the presence of six rays is regarded as a generic character. 



The arrangement of the wheels is also of interest. At the anterior end of 

 the body they are confined to the round papillse, each of which contains on an 

 average about thirty wheels. Towards the middle of the body, where the 

 papillse seem to run together, the wheels are accordingly collected mainly in 

 larger aggregations of somewhat vermiform shape, and in addition a few 

 wheels occur isolated in the body-wall, thus giving a condition intermediate 

 between Chirodota and Ludwig's genus Trochodota. Towards the posterior 

 extremity the papillse (now round again) become more definite and are 

 arranged concentrically around the anus. 



(ii.) Short and thick curved rods (fig. 11 />) slightly expanded at both 

 ends, which are covered with short spines. The average length of these rods 

 is O'l mm., and thickness 0*016 mm., but they vary both in size and shape. 

 Their ends are occasionally bifurcate. 



These spicules are concentrated along the radii as five wide bands, one 

 outside each longitudinal muscle, but also occur scattered about the inter- 

 radial areas. 



(iii.) Smooth slender curved rods (fig. 11 A), frequently with slightly 

 branching ends. The average length is about 0'065 mm., and thickness 

 0*005 mm. ; but they are very variable both in size and shape. These 

 spicules are confined to the tentacles, where they form two rows in each 

 branch of each tentacle. 



(iv.) Short thick rods, with smooth and rounded ends (fig. 11 a), sometimes 

 known as miliary granules. A fairly large example of these is 0*035 mm. in 

 length and 0*01 mm. in thickness, but they vary enormously in size. These 

 spicules are restricted to the radii, where they form two bands (each two or 



* Dendy, Journ. Linn. Soc, Zool. vol. xxvi. 1897, pp. 49-50, figs. 1-6. 

 t Ludwig, Zeitschr. f. wiss. Zool. pp. 350-353, pi. 16. figs. 1-9. 



o* 



