EXPLANATION OF THE PLATES. 



To avoid useless repetitions in the description of the Figures, the same letters are used, throurjhout these Plates 

 [I. -VIII.], to denote identical parts. It will greatly facilitate the reading of this memoir to heconie familiar with 

 the notation here adopted. 



Explanation of the Lettepjng on Plates I. -VIII. 



a, anus. 



6, dorsal or water pore, madrejioric opening. 



c, alimentary canal. 



d, digestive cavity, stomach. 



d', abactinal water-tubes in angle of rajs of young 

 Starfish. 



d", water-tubes of lateral hne of rays of young Star- 

 fish. 



d'", water-tubes of median line of rays of young Star- 

 fish. 



e, eye of Starfish at base of odd tentacle {I'), 

 e', median anal arms of Bracliiolaria. 



«", dorsal anal arms of Bracliiolaria. 

 e'", ventral anal arms of Brachiolaria. 

 e"", dorsal oral arms of Brachiolaria. 

 e^, ventral oral arms of Brachiolaria. 

 e', odd terminal oral arm of Brachiolaria. 

 y, brachiolar arms. 



f, branch of water-tube (w id') leading intoy^ 

 /", odd brachiolar arms. 



/'", surface- warts at base of odd brachiolar arra (/"). 



h, hole of cul de sac of water-tube w. 



I, central abactinal plate of yoimg Starfish. 



'ij ^11 'i)   interbrachial abactinal plates of young 



Starfish. 

 2, I2, l^, • . brachial plates of young Starfish. 

 m, mouth. 



m', pistol-shaped oral pouch of oesophagus. 

 m", anal pouch of oesophagus, 

 n, opening for passage «f ambulacral sucker. 

 0, oesophagus. 



p, spines on edge of ray of Starfish. 

 pi, spines of exterior rows along abactinal surface of 



rays. 

 P2, spines of middle row on abactinal surface of rays. 

 Pa, central spiue of abactinal surface of Starfish, on 



central plate (l^). 



Pc, plate at jimction of adjacent rays (ovarian plate). 



p', ])", different forms of pedicellarijE. 



r, abactinal surface. 



r', first set of five limestone rods which appear on 



abactinal surface, and which eventually become 



the brachial plates (/j). 

 r", second set of five interbrachial limestone rods, 



which eventually become the interbrachial plates 



r'" -)■"', rays of young Starfish; r'l' being ray next 

 to madreporic body, when Brachiolaria is seen 

 from the dorsal side. 



s t and s, actinal region. 



t, t, t, . . tentacles of the young Starfish. 



t', odd tentacle. 



t", ambulacral tube. 



u, lateral ambulacral plates, siu-mounted by spine. 



u', mc<lian ambulacral plates with very small spines. 



V, vibratile chord, anal part. 



v', vibratile chord, oral part. 



!(', water-tube, developing abactinal area. 



ic', water-tube of Brachiolaria leading to madreporic 

 opening (i), developing actinal area. 



w tv', portion of water-tube of Brachiolaria formed by 

 junction of w and w'. 



In all the figures of the Brachiolaria (Plates L-IV.), 

 the attitude which has been given to them is not 

 a natural attitude. This has been done pur- 

 posely, for the sake of making the comparison 

 with the memoirs of Miiller easier. The only 

 figure of a Brachiolaria which is in its natural 

 attitude is that of PI. VIII. Fig. 8. The young 

 BracliioLiria does not, however, move with the 

 anal part below, till the latter is loaded down by 

 the development of the Starfish, and we see 

 them swimming about, before that time, almost 

 in every possible attitude. 



