EXPLANATION OF THE PLATES. 



(23) 



Fig. 3. Little older than fig. 2, and stretched longitudi- 

 nally. Letters the same as in the last. 

 Fig. i. The radiating tubes beginning to develop. 



Z' ri 



Fig. D represents fig. 4 in outline, a inner and b outer wall of the hydra. 

 — c f I (-2 c3 the four radiating tubes. — ch channel of c. — d outer wall 

 of the medusa, //l /^ edge of the inner wall in which c c^ are hollowed. 



F\ff. 5. A little furtlier advanced than iijjr. 4. 



Fig. E. 



5 in outUne. a inner and & outer wall of the hydra, 

 outer and c inner sides of the radiating canal. — ff^ edge of 

 inner wall. — d outer wall. 



FijT. G. A little older than fin 



Fig. F represents fig. 6 in outline. 

 — c abroad radiating tube scei 

 outer face of the radiating tube! 

 of the radiating tubes. 



inner and b outer wall of the hydra. 

 )ni its outer face. — fi inner and c- 

 profile. — ^/ outer wall.— g-g-i base 



Fig. 7. Sectional view of fig. 6, to show the projection 

 {iP) of the outer wall into the cup-like hollow of the 

 inner wall (c). a inner and h outer wall of the 

 hydra. As this figure was drawn for the purpose 

 only of showing how the outer wall projects into the 

 hollow of the inner wall, no special references are 

 needed to the other parts, which, by comparison with 

 fig. 6, explain themselves. 



Fig. 8. Considerably older than figs. 6 and 7, showing 

 the prolongation of the horn-like sheath over the disc, 

 and the broad radiating tubes. 



FiK. G. 



Fig. G represents fig. 8 in outline. In the plate the proboscis (h) is omitted. 

 a inner and b outer w[),ll of the hydra. — c outer and ci inner face of 

 the radiating tubes, in profile. — c2 a broad tube next the eye. — d 

 outer wall of the disc. — g base of the radiating tubes and the proboscis 

 (A) in profile. — g^^ ir2 outlines of the wall where the proboscis and the 

 tubes meet. — i horn-like sheath. 



Fii:^. 8*. View of the actinal end of fi^. 8. 



Fig. II represents fig. Sa 

 wall. — ^■ edges of r. - 

 wall. — h the 



the radiating tubes. — (/ the outer 

 »(! outer surface of the innermost 



Fig. 9. A little older than fig. 8, showing the lateral 

 projection of the radiating tubes preparatory to the 

 formation of the circular tube, a a^ inner wall of the 

 radiating tube; h b- outer wall of the disk; 1^ outer 

 wall of radiating tube near the edge of the disk ; c the 

 same as i\ but near the abactinal end; I the lateral 

 projections from the radiating tubes ; n the proboscis. 



Fig. I represents a sectional view of fig. 9 at a point between the radiating 

 canals. — a the middle wall. — n'-^ edge of a. — & outer wall, continuous 

 at 62 with the innermost wall (b'i). — d digestive cavity. —ir outer wall 

 of the proboscis, continuous with 61. — n^ inner wall of the proboscis con- 

 tinuous with«. 



