EXPLANATION OF THE PLATES. 



(7) 



sheath ; l!' the terminal expansion of i' ; </ the mc- 

 dusiB ; r the branching base of the stem ; t the coro- 

 nal tentacles ; t- (' the buccal tentacles. 8 diameters. 



Fig. 8*. View of the abactinal side of the head of a 

 hydra. i' \? d as in fig. 8; ( i? t* f coronal tenta- 

 cles in various stages of growth. 8 diameters. 



Fig. 18. The retiform stolonic basis of the hydra of 

 Hydractinia polyclina. a the outer wall at the edge 

 of the depressions (il) ; h inner wall ; h' granules 

 circulating in the channels; c cells of a, in profile; 

 fl depressions in the outer wall, which sometimes appear 

 to be open spaces. 40i) diameters. 



PLATE XXVn. 



Figs. 1-7, BOUGAINVILLIA SUPERCILIARIS Af/. ; Figs. 8 



and 9, Clytia cylindrica Ag.; Figs. 10-26, Tiioa 

 (Eudendrium) dispar Ag. 



(Kigs. 1, 8, 9, 10, 11, 12, 1.3, 22, 2.3, 24, 25, 2(3, Jrawn by A. 

 Sonrel: the others by 11. J. Clark,] 



Fig. 1. A hydromcdusariura. Natural size. 



Fig. 2. A portion of fig. 1 . a-d rings of the stem ; 

 A B medusa-buds. 2."> diameters. 



Fig. 3. The head of a hydra and the upper part of 

 a branch of fig. 1. a outer, and h inner wall of the 

 head ; a' outer, and 6' inner wall of the proboscis ; 

 a} outer, and ¥ inner wall of the tentacles; c the 

 horn-like sheath ; c' the termination of c ; d digestive 

 cavity ; m mouth ; ( «' tentacles. 200 diameters. 



Fig. 4. A young head of a hydra, almost ready to burst 

 its envelope. a outer, and b inner wall ; a" outer, 

 and li' inner wall of the proboscis; a- outer, and h' 

 inner wall of the tentacles ; c c' the horn-like sheath ; 

 d digestive cavity. 300 diameters. 



Fig. 5. A medusa-bud and the pedicel. a outer, and 

 h inner wall of the pedicel ; c inner wall of the me- 

 dusa, containing the radiating tubes ; i the horn-like 

 sheath. 300 diameters. 



Fig. G. A bud considerably older than fig. .5. c c' horn- 

 like sheath ; I base of c. 300 diameters. 



Fig. 7. A medusa-bud in which the circular tube (/) is 

 nearly complete, abed' i as above ; / circidar tul>e ; 

 n the proboscis. 300 diameters. 



Fig. 8. The medusa of Clytia cylindrica, seen from below, 

 o the edge of the opening in the veil; b the circular 

 tube; c the tentacles; c' the tentacles budding; c- 

 the base of c; d the proboscis; e the radiating tubes; 

 e' the genital organs; / ocular organs. 40 diameters. 



Fig. d. The same as fig. 8, seen obliquely from below, 

 g the disk. 



Fig. 10. A branch of Tlioa dispar: the male. A A 

 young head ; 15 heads destitute of medusoids ; C me- 

 dusiferous heads. 25 diameters. 



Fig. 11. A head from fig. 10. p the probo-scis. 2.5 diams. 



Fig. 12. A head from fig. 10, bearing young medusas. 

 md medusa?; p the proboscis; ( the tentacles. 40 diams. 



Fig. 13. Similar to fig. 10, C. d base of the medusa 

 pedicel; <Z' the digestive cavity; md medusa;; ]) the 

 proboscis. 40 diameters. 



Fig. 14. An incipient medusa-bud from fig. 10. a outer, 

 and b inner wall ; c chymiferous cavity. 300 diameters. 



Fig. 15. A little older than fig. 14, with the same let- 

 ters. 300 diameters. 



Fig. 1(). From fig. 10: the primary medusa. a outer, 

 and h inner wall cif the pedicel ; a} disk ; ca disk 

 cavity ; p proboscis. 300 diameters. 



Fig. 17. A medusa much older than fig. Kj. Letters 

 as in fig. IG, and / lasso-cells. 300 diameters. 



Fig. 18. The primary (A) and secondary (B) medusa, 

 far advanced, the tertiary medusa (C) just forming. 

 a outer, and b inner wall ; c:' the inner, or a.xial wall ; 

 ca disk cavity containing the spermatic mass; e con- 

 striction between A and B ; e' constriction between 

 B and C; p proboscis; p' the homologue of p. 300 

 diameters. 



Fig. 19. An exterior view: the primary medusa (A) 

 nearly mature, the secondary (B) and tertiary (C) 

 far advanced. The letters as in fig. IS. 300 diams. 



Fig. 20. A, an immature spermatic particle from fig. 19, 

 A: 500 diameters. B, diagrammic, to show the form. 



Fig. 21. A, a mature spermatic particle: 500 diameters. 

 B, a diagrammic figure, to show the form. 



Fig. 22. A head and branch of a female hydromedu- 

 sarium. a b the young medusa;; md md' nearly ma- 

 ture medusa; ; p the proboscis ; t coronal tentacles. 

 25 diameters. 



Figs. 23, 24, and 25. The same as fig. 22, with corre- 

 sponding letters. 40 diameters. 



Fig. 2G. A view from above of fig. 22. dc the disk ; 

 m the mouth; p proboscis; t coronal tentacles. GO 

 diameters. 



PLATE XXVm. 



Clyti.a poterium Ag. 

 [Figs. 1 and 2, drawn by A. Sonrel; the others by H. ,1. Clark.] 



Figs. 3, 4, 5, G, 7, 8, 9, 10, 13, 13^, 15, and 19, are mag- 

 nified 100 diameters; figs. 11, 12, and 14, 200 diameters; 

 fig. IG, GO diameters; figs. 17, 17a, 18, and 20, B C, 

 500 diameters; fig. 20, A, diagrammic. 



