EXPLANATION OF THE PLATES. 



In order nut to spoil the appearance of any of the most delicate and of the smallest figures drawn upon the following plates, which 

 require a large number of signs to explain their details, I have only added special references to the largest of them, or to 

 those which would not he injured by crowded marks of every kind; but, to supply this deficiency, I have had wood-cuts made 

 corresponding to the figures requiring the most minute explanations, and trust that the others will explain themselves by comparison. 



PLATES I. aiul U. 



Idyia roseola Aij. 



[All the figures of these Plates were drawn from nature by A. Sonre!.] 



Plate I. requires but little explanation. It represents Iiljia 

 roseola in different stages of growth and in different 

 attitudes, in the size of life, and with its natiu-al 

 colors. 



Figs. 1-3 represent adtdt specimens; figs. 4 to 10 arc not 

 full grown ; fig. 6 is a young, magnified in fig. Ca. 



Fig. 1 is a view from the narrow side of the body, 

 showing tlie two anterior or posterior ambulacra and 

 two of the lateral ambulacra, one on each side of the 

 figure. The cirenmscribed area is visible, but fore- 

 shortened, as it trends at right angles with the surface 

 represented. 



Fig. la shows how the lips may close up. 



Fig. 2 represents the same animal from the broad side 

 of the body, showing the two lateral ambulacra of one 

 side in the centre of the figure, and two of the an- 

 terior and posterior pairs, one on each side of the 

 figure. On the abactinal side the lateral interambu- 

 lacrum rises above the level of the circumscribed area, 

 which trends in the plane of the figure. 



Fig. 2a represents the mouth turned sideways, showing 

 the linear arrangement of the epithehum lining the 

 interior of the digestive cavitv. 



Fig. 3 represents the abactinal side of the body as it 

 appears when fully distended by the filUng of the chy- 

 miferous system. In the centre appear the circum- 

 scribed area and the eye-speck, towards which trend 

 the eight narrow bands extending from the sunmiit of 

 the ambulacral rows of locomotive flappers to the eye- 

 speck. On the sides of the circumscribed area, nearl)- 

 midway of its two halves, the cceliac apertures may 

 be seen. Nearly concentrically with the abactinal 

 termination of the locomotive flappers, the outline of 

 the digestive or coeliac cavity may faintly be seen 

 through the thickness of the spherosome, as well as 

 the eight ambulacral tubes which trend in the direction 

 of the locomotive flappers and the coeliac tubes which 

 run between the lateral ambulacra, and are seen pro- 

 jected beyond the outlines of the digestive cavity. The 

 deep pink rows on the sides of the locomotive flappers 

 are formed by the accumulation of pigment cells over 

 the spermaries, while the paler rows on the opposite 

 sides of the ambulacra indicate the ovaries. 



Fig. 4 is a view from the actinal side with the month 

 shut in a straight line. The outlines of the digestive 

 cavity and the chymiferous tubes are visible through 

 the thickness of the spherosome. The cadiac and the 

 oral tubes are particularly distinct. 



Fig. 5 represents a half-grown specimen from the broad 

 side, with the actinal end of the body turned inside 

 into the digestive cavity, in conse(piencc of which the 



(1) 



