(26) 



EXPLANATION OF THE PLATES. 



Fig. 11. About the same age as tig. 10, showing the 

 radiating tnlie « c' ir to bo distinct from either the 

 outer ((•) or the innermost wall (Jj) ; d stria; of h. 

 500 diameters. 



Fig. 12. Part of the disk of a medusa only a day or 

 two old ; after being iu aleohol ; a dotted strias of the 

 innermost wall ; «' the same as a in profile ; b blister- 

 like projections of the cells of the same wall; // the same 

 as h, iu profile ; c outer surface of the disc. 500 diams. 



Fig. 13. Inner face of the disk and radiating tube of a 

 medusa just set free. a cells of the innermost wall ; 

 b the same as c, covering the tube (c). 500 diams. 



Fig. 14. From a medusa ready to drop from tlie 

 hydra ; the edge of the disk was involuted so as to 

 bring its thickness into sharp profile ; a outer wall ; 

 a' cells of o; b middle wall, continuous wilh the 

 inner wall of the hydra, and the same as the inner 

 wall of the very young medusa; b' thickening of /; 

 where it embraces the radiating canal if, whicli is 

 hollowed out in it ; c innernvost wall ; <■' the pajiil- 

 late cells in profile ; c- the same as c in the distance ; 

 d radiating canal passing into the distance; rf' the same 

 as d in transverse section; e the horn-like sheath. 4o0 

 diameters. 



Fig. 14". Cells from the outer wall of a medusa of the 

 same age as fig. 14. a the cell wall or ectoblast ; 

 b the mcsoblast; c the entoblast. 500 diameters. 



Fig. 14''. Cells of the innermost wall of the same 

 medusa as those of fig. 14a. 500 diameters. 



Fig. 15. The proboscis of a medusa two or three days 

 old. Superficial and jirotile views coud lined in one 

 figure, as one may see it merely by changing the 

 focus ; e radiating tubes nearest the eye ; e' the same as 

 e where they open into the digestive cavity ; g outer 

 wall of the ]iroboscis, which at (/' Ijcciimes the inner- 

 most wall of the disk ; // the large wedge-shaped cells 

 of the inner wall, in profile ; /;' the same as /( iu a 

 superficial view ; P the same as /( and /;' where it be- 

 comes the middle wall of the disk ; and Ji^ where it 

 becomes the wall of the radiating tube (/:) ; A' the 

 remains of the same wail when it has formed the inner 

 wall of the peiluncle; //'' where Ji divcrgi'S to firm a 

 broad space fir the digestive cavity of the di>k ; / 

 cavity of the proboscis; /.■ lasso-eells ; m to ?«' longitu- 

 dinal furi-ows upon the outer wall of the proboscis ; 

 71 the outer wall of the ilisk dragged inward by the 

 retraction of the adherent inner or middle wall (//'); 

 »' parietes of the outermost wall of the disk around 

 the drprcssion formed by the inflection of ti. 500 

 diameters. 



Fig. 10. Base of the proboscis and the neighboring 

 centre of the disk of a medusa a little younger than 

 fig. 15, and with the same lettering; beside which e' 

 is the wall of e; i} digestive cavity of the disk. 400 

 diameters. 



Fig. 17. Edge of the disk and the base of a tentacle 

 of a medusa aliont as old as fig. IG. a pai'letes of 

 the disk ; a" tr outer wall of the tentacle ; b the thick 

 irregular wall of the radiating tube ; i' the circular 

 tube ; h" the junction of b and 6\ or the bulb cavity ; 

 i' inner wall of the tentacle continuous with b h^ ; c 

 (•' innermost wall of the disk ; (/ the eyo-speek. 400 

 diameters. 



Fig. IS. Exterior face view of the liase of a tentacle 

 and its bulb cavity ; fi-om a medusa three days old. 

 a. eye-speck; b inner wall of the bulb, or point of 

 junction of the radiating ('.) and circular (</) canals; 

 c outer wall of the Vmtb ; /' projection of the disk 

 over the base of the tentacle ; (/ outer wall of the 

 tentacle ; Ji inner wall of the tentacle ; / cavity of 

 the tentacle; k lasso-eells; I bulb cavity. 4oo diams. 



Fig. 10. The same as fig. is, seen from above, with the 

 same letters ; showing the truncate cone (</) of the 

 eye-speck. 500 diameters. 



Fig. 20. View from above of the digestive cavity of 

 the disk of a medusa three days old. a the diges- 

 tive cavity; b radiating tubes; c wall of b; c^ where 

 the wall of b passes into the inner waU of the pro- 

 bo.s(is (</) ; c' innermost wall of the disk; c' the thick 

 inner wall at the base of the proboscis, continuous 

 with c, but seen in the distance. 500 diameters. 



Fig. 21. Cells from the outer surtace of the disk and 

 veil of a medusa probably two or three days old ; 

 they are slightly swollen liy fresh water. 500 diams. 



Fig. 22. The same as fig. 21, in a natm-al state, a 

 the mcsoblast; b the entoblast. 500 diameters. 



Fig. 2.'i. The same as figs. 21 and 22. Cells of the in- 

 nermost wall of the veil seen from the outside and 

 through the concentric stria" oi' the middle wall. 

 They are a little changed by alcohol. 500 diameters. 



Fig. 24. Cells of the innermost wall of the disc, through 

 which are seen the horizontal stria; of the middle 

 wall. a the mcsoblast. 500 diameters. 



Fig. 25. Lasso-cells upon the tentacular bull) of a full- 

 grown free medusa. 500 diameters. 



Fig. 2tl. The same as fig. 25. Tiie cells of the outer 

 wall of the tentacular liulb. 500 thameters. 



Fig. 27. The same as figs. 25 and 2G. Cells of the 

 radiating canal brought out by fresh water. a iacc 

 view ; b in profile. oOO diameters. 



