746 PB. W. B. CAEPENTER ON THE STBUCTUBE, PHYSIOLOGY, AND 



(§ 54), I cannot think it likely that it is displaced from time to time by the interposi- 

 tion of a new segment between itself and the brachial. The most probable place for 

 such interposition seems to be either between the basal and the second segment, or be- 

 tween the penultimate segment and the terminal claw-bearing segment. Since no such 

 traces of incompleteness present themselves in the segments which follow the basal as 

 would justify the former supposition, we seem compelled to adopt the latter ; and it is 

 not a little curious that the increase in the number of segments in the Stem, the Dorsal 

 Cirrhi, the Arms, and the Pinnules should thus take place in different modes, — the new 

 segments making their appearance in the Stem immediately beneath its highest segment 

 (§ G3), in each Dorsal Cinhus at its base (§ GG), in each Arm at its termination (§ 67), 

 and in each Pinnule at the base of its terminal segment. 



Explanation of the Plates. 



PLATE XXXI. 



Side view of Antedon rosaceiis attached by its dorsal cirrhi to a stone ; drawn from a 

 living specimen in a Vivarium. — Magnified S^ diameters. 



A, Disk and basal portion of the Arms of the same, as seen from above ; showing the 

 manner in which the basal pinnules arch over the ventral surface of the disk. — Magni- 

 fied 3^ diameters. 



PLATE XXXII. 



Fig. 1. Dorsal aspect of the Calyx oi Antedon rosaceus, as seen after the removal of the 

 dorsal cirrhi : — c, Centro-dorsal plate, entirely concealing the First Eadials ; 

 r^, r^, Second Radials ; r*, '/•^ Third or Axillary Radials ; br\ br\ First 

 Brachials. — Magnified 8 diameters. 



Fig. 2. Ventral aspect of the Calyx, as seen after the removal of the visceral mass. 

 Around the central depression is seen a circlet oifive pairs of Muscles, passing 

 between the First and Second Eadials ; and outside these is a circlet of ten 

 pairs, passing between the Third Radials and the First Brachials (see Plate 

 XXXIV. fig. 2).— Magnified 8 diameters. 



Fig. 3. Ventral surface of the Visceral Disk, showing the mouth, m, in the centre, with 

 five channels radiating from it, which form by their bifurcation the ten 

 channels that pass along the Arms and give off branches to the Pinnules, the 

 first and second of which on each arm assist in supporting the \isceral mass ; 

 at a is shown the Anus seated on a proboscis-like funnel that rises between 

 two of the Radial channels. — Magnified 8 diameters. 



Fig. 4. Dorsal Cirrhi as seen radiating from the Centro-dorsal plate, c, to which they ai'e 

 articulated. — Magnified 15 diameters. 



