(2) 



EXPLANATION OF THE PLATES. 



Fiu, 



gent'ral fonn appoars more rounded than umler ordinary 

 cii'cumstances, as may be seen upon comparing iig. 5'', 

 ■which represents the same animal in the same con- 

 dition from the actinal side with fig. 4, in whicli the 

 moutli is visil)le. 



;. (! is a \iew of a young specimen, as they appear 

 early in Jidy, magnified in fig. C, to show more dis- 

 tinctly that the short rows of locomotive flappers leave 

 the anibidacral tubes uncovered for half the height of 

 the bully, and that the ramifications of these tubes are 

 much fewer and much more sim[ile than iu older 

 individuals. 



;s. 7 and f> represent one and the same specimen, about 

 half grown, from the side in fig. 7, and from the anterior 

 or posterior surface in fig. 8. The locomotive flappers 

 extend ahvaily much nearer the mouth than in fig. 

 C, and the ramifications of the ambulacral tubes are 

 more lunnerous ; but the whole body is still much paler 

 than that of adult specimens. 



;. !) is a view of the mouth, contracted in the centre 

 and gaping forward and backward. 

 :. Ill represents a specimen gorged with a Bolina nearly 

 as large as itself, distorting its form to so great an extent 

 as barely to resemble another view of the same, given 

 in fig. 7. 



.\TE II. represents structural details of Idyia roseola. 

 :s. 1 and 2 show the difference there is in the ajipear- 

 ance of the abactinal end of the body when seen from 

 its broad or narrow side. Fig. 1 shows the broad or 

 lateral side, with the lateral si)heromere and especially 

 the lateral interambulacrum bulging above the anterior 

 and posterior pairs, and concealing partly the circum- 

 scribed area, which however shines through, with the 

 eye-speck in the centre. Fig. 2 shows the narrow 

 anterior or posterior side, ■with the eye-speck and the 

 foreshortened circumscribed area visible in the trough 

 formed by the depression in the abactinal termination 

 of the anterior and posterior spheromeres. 



a magnified view of the abactinal j)oIe, repre- 

 senting the position of the eye-speck iu the centre of the 

 abactinal area, between the anterior and the posterior 

 halves of the circumscribed area, and with the central 

 termination of the eight narrow bands extending from 

 the summit of the locomotive flappers to the eye-speck. 

 The gray bands forming a zigzag around the eye are 

 the outlines of the funnel. 



;. 4 represents a magnified liaiid across one ambulacrum 

 aud part of another. Right and left of the row of 

 locomotive flappers arc the ovaries and the spermaries ; 

 the first covered ■n-ith deep piuk-c-olored pigment cells. 



and the latter only lined with paler pigment. Another 

 row of ovaries belonging to the adjoining ambulacrum 

 is seen in the same interambulacrum, and the inter- 

 vening part of the spherosome is traversed by numer- 

 ous branches of the ambulacral tube, arising partly 

 from the ovarian pouches and partly from the tulie 

 itself. Along the spermaries there are no ramifications 

 of the chymiferous tubes. 



Fig. 5. The abactinal end of the ambulacrum of a 

 younger specimen, in which the ovaries and spermaries 

 are not yet developed, more highly magnified, in 

 order to show the trend of the cells of the radiating 

 system. 



Fig. C. Ramifications of the chymiferous tidies of an adult 

 specimen more highly magnified, to show to what extent 

 the eggs may bi' crowded in these tubes, after they 

 have left the ovaries. 



Fig. 7 gives an obliipie view of the cieliac bulb, rising 

 upon tlie side of the circumscribed area. The lower 

 part of the figure represents a jiart of the sin-f;vce of 

 the area itself with its marginal fringes, to show that 

 the cadiac Indb is outside the area, as is again shown 

 in fig. II. where the cadiac aperture is represented gaping, 

 in the shape of a circidar hole. 



Fig. 8. I'rofilc view of the eye-speck with its transparent 

 cap, magiufied and seen from the broad side of the 

 bod}-, so that only four of the narrow bands are visible 

 below it, and part of the circumscribed area in profile. 

 This figure corresponds exactly to fig, 3, which repre- 

 sents the same parts, aud iu the same size, from 

 above. 



Fig. 9. Circumscribed area on one side of the eye ; seen 

 obliquel)-, in order to show at the same time its entire 

 outline, the surface encircled by its fringes, the cteliac 

 aperture on its side, and the narrow baud of one of 

 the anterior ambulacra following its outline. 



Fig. 1(1. Vertical section of the whole body, in the ili- 

 rection of the longest or axial diameter, with the exception 

 of the abactinal side, through which jiasses a transverse 

 section reaching the digestive cavity. The ailjoining 

 wood-cut (fig. A), which represents only the abactinal 

 part of fig. 10, n. II., may best explain the j)arts so 

 brought into view. The actinal part of fig. m shows 

 the priilongatlou of the parts cut through in fig. A, 

 one half of the mouth and one half of the oral tube 

 being cut through in the anterior anil in flic posterior 

 intcrambulacra, and the lumen of the oral tube ap- 

 pearing in the thickness of the spherosome. The epi- 

 theliel lining of the digestive cavity appears as vertical 

 striiv aljove the margin of the mouth. 



