EXrLAXATION OF THE PLATES. 



(3) 



r ri cceliac tiO'- ' i- ■ iit ti-ar its origin. — 1^ 1^ lateral ambulacral tubes, cut 



near their origin ^ /- anterior and posterior ambulacral tubes, cut near 



their origin ; all the cut ambulacral tubes are on the same side of the 

 body ; on the opposite side the following organs are Tisible from their 

 internal face : — l"^ l^ anterior and posterior ambulacral tubes. — l^ t* lat- 

 eral ambulacral tubes. — aaaa represents the section of the sphi 



Fig. 11. Profile view of an aiiibulaeral tube, with three 

 rows of e.xtended locomotive flappers and a band of 

 pigment cells upon the spermaries projecting as pouches 

 from that side of the tube. 



Fig. 1 2. Oblique view of seven rows of locomotive flappers, 

 greatly curved. 



Fig. 13. Magnified view of an amljulacral tube, with four 

 rows of slightly arched locomotive flappers, and the 

 incipient pouches of the spermaries partly covered by 

 pigment cells. 



Fi". 14. Abactiual tennination of an ambulacrum, to show 

 how rapidly the rows of locomotive flappers taper on 

 that side, in comparison with their actinal termination, 

 as represented in fig. 17. 



Fig. I.5. Profile view of an ambulacral tube, with five 

 rows of slightly arched locomotive flappers. The ad- 

 joining interambulacrum is so raised that the row of 

 pigment cells covering the spermaries is seen in profile, 

 while in fig. 13 it is depressed and the whole diameter 

 of the tube is visible. 



Fig. It). Profile view of the ambulacral tube of an aduli, 

 specimen, slightly magnified, with the adjoining inter- 

 ambulacrum depressed so that the ovarian pouches are 

 fully seen. As these organs and the spermaries are 

 on opposite sides of the ambulacral tubes, the loco- 

 motive flappers appear curved in a different direction 

 in fig. IG and in fig. 13, as they are seen in opposite 

 directions. 



Fig. 1 7. Actinal prolongation of the row of locomotive 

 flappers, tapering to a mere thread and surrounded by 

 branching pigment cells. Here the underlying ambu- 

 lacral tube, from which arise two small branches on 

 the same side, is much broader than the row of flap- 

 pers. It is interesting to notice, that even in the 

 prolongation of the tube beyond the ovaries and the 

 spermaries, the pigment cells are much more crowded 

 on the spermatic side of the tube than on the oppo- 

 site side, and that the branches extending into the 

 spherosome arise only on its ovarian side. 

 VOL. Ill, 39 



Fig. 18. This figure is reproduced in the adjoining wood- 

 cut, fig. B. It represents the abactinal pole of our 

 LUna in profile and sufficiently magnified to show the 

 relations of the central chjTniferous cavity to the ambu- 

 lacral and coeliac ch}'miferous tubes, to the forks of 

 the funnel, and to the coeliac aperture. 



a capsule of the eye-speck. — h eye-speck. — cc circum.ecri>>ed area. — d 

 coiliac aperture. — e tubercle of the eye-speck. — // forks of the funnel. 

 — g opeiiiDg of the coiliac tube. — r cceliac tube itself. — hh narrow pro- 

 longations of the rows of locomotive flappers. — P l^ anterior and posterior 

 ambulacral tubes with the flappers of ^2, — ;8 l\ lateral ambulacral tubes 

 with their flappers. — t^t^ internal ramifications of the ambulacral tubes. 



Fig. 19 is fuUy explained on ])age 281 of the te.xt. 



PLATE Da. 



PLErnoBR.\ciri.\ riiododactyla. 



[Figs. 1 to 19, and 21, 23, 24, and 26, drawn fi-om nature by H. 

 J. Clark, the others by A. Sonrel.] 



A, B, C, D, E, F, G, H, the eight broad interambidacra 

 trending from the actinal to the abactinal poles : in figs. 

 20, 21, 22, and 23, they are placed correspondingly, 

 A and E in the plane of the digestive ca-inty, and 

 C and G in the tentacular plane. These letters also 

 mark the position of the eight interambulacral bands 

 of the peripheric cellulo-motor system, which are shown 

 in a transverse section at the equatorial region. 



a, the mouth. It assumes the most diversified outlines when 

 shut, or expanded in various ways. 



a', the corners of the mouth, or the edge of the digestive 

 cavity, seen in the distance. 



h, the actinal part of the digestive cavity. 



c, the abactinal part of the digestive cavity upon the 

 walls of which exist the brown hepatic cells, through 

 which the substances which have been digested are 

 emptied into the maifi chymiferous cavity </• There 

 is, at its bottom, an opening c'. 



(7, central chj-miferous cavity. This cavity with its vertical 

 prolongation f corresponds truly to the main cavity of 

 Polii-pi, with this difference, that in Poh-pi there are 

 partitions dividing it off" around the periphery, while 

 in Medusaj the mass of cells forming the body occupies, 

 to a great extent, the inner space of the animal, and 



