EXPLANATION OF THE PLATES. 



(5) 



PLATE XXIV. 



TUBULAEIA COUTHOUYI Ag. 

 [Figs. 1-5, drawn by A. Sonrel; the others by H. J. Clark.] 



Figs. 6-13 magnifi,ed 200 diameters; figs. 14-18 and 24- 

 26, 100 diameters; fig. 19, 00 diameters; figs. 20-23, 

 40 diameters. 



Fig. 1. A group of female hvdroids, natural size. a 

 the stem ; h the medusaa ; p the proboscis ; t the coro- 

 nal tentacles. 



Fig. 1, B. A lateral view of the head of a hydromedu- 

 sarium, magnified 5 diameters. a the sterh ; n' the 

 largest tubule ; b the terminal expansion of the stem ; 

 c the base of the head; d rf' the medusse; e the 

 mcdusiferous branches ; t coronal tentacles. 



Fig. 1, C. The same as fig. 1, B, seen from the under side. 



Fig. 2. A male hydroid, with the proboscis (^) spread 

 wide open. The letters as in fig. 1. 



Fig. 3. Another male hydroid, the head hanging down- 

 ward. Letters as before. 



Fig. 4. The proboscis of a male hydra. a the base ; 

 t (' i° fi the tentacles. 5 diameters. 



Fig. 5. The broadly-expanded proboscis and a medusife- 

 rous branch of a male hydromedusarium (d e). a the 

 base of the proboscis; b the decurrent bases of the 

 tentacles (J i') ; d the oldest, e the youngest medusa;. 

 5 diameters. 



Fig. G. A medusa-bud, just beginning to form, a outer, 

 and b inner wall ; d chymiferous cavity. 



Fig. 7. A, a double-walled hernia-like medusa, a' outer, 

 and J' inner wall ; d chymiferous cavity. B, a far 

 advanced bud. n' outer wall ; c ends of the radi- 

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

 tubes; / germ-basis. 



Fig. 8. A little younger than fig. 7, B. The letters 

 the same. 



Fig. 9. An exterior view, a little younger than fig. 7, B. 

 The letters the same. 



Fig. 10. An interior view, showing three of the radi- 

 ating tubes (c c'). The letters as in fig. 7, B. 



Fig. 11. A little older than fig. 7, B, and with the same 

 letters. 



Fig. 12. The circular tube is formed. a b c as before; 

 a} outer wall of the disk; J' inner wall containing 

 the radiating tubes; d base of the radiating tubes and 

 proboscis (</'). 



Fig. 13. A male medusa, a little older than the last, 

 with corresponding letters, and also c', junction of radi- 

 ating and circular tubes, seen in the distance, and </, 

 spermatic mass. 



Fig. 14. A nearly mature female medusa. c remains 

 of the circular tube ; d proboscis ; e radiating tube ; 

 / germ-basis. 



Fig. 15. The chymiferous tubes obliterated, and the germ- 

 basis (ff^) beginning to divide, a a} b b^ d as in 

 fig. 12; W the base of the proboscis. Drawn as a 

 sectional view. 



Fig. 16. The germ-basis, still further divided. a b f f^ 

 as in fig. 15; c as iu fig. 14. 



Fig. 17. A sectional view of a medusa of the same age 

 as that of fig. 16. The letters as in fig. 15, and c as 

 in fig. 14. 



Fig. 18. The germ-basis nearly all divided off into hydrae 

 (/' /O- " outer, and J inner walls of the pedicel ; 

 c junction of circular and radiating (e) tubes ; d pro- 

 boscis. 



Fig. 19. Similar to fig. 18, but not so far advanced. 

 / germ-basis. 



Figs. 20, 21, 22, and 23. Similar to figs. 18 and 19, with 

 the same letters. 



Fig. 24. The hydroids have escaped, but more of the 

 germ-basis remains. Letters as in figs. 18 and 19 : 

 also a' the wrinkled disk. 



Figs. 25 and 25*. Lateral and end view of an empty 

 medusa. Letters as in fig. 24. 



Fig. 26. A male medusa, a outer, and h inner wall of 

 the pedicel ; c £is in fig. 14 ; / spermatic mass ; y 

 disk cavity. 



PLATE XXV. 



Hybocodon prolifer .417. 



[Figs. 1, 2, 15, 15a, and 15b, drawn by A. Sonrel; the others by 

 H. J. Clark.] 



Fig. 1 natural size; figs. 2 and 3 magnified 10 diameters; 

 figs. 21, 14, 14»-, 15, 15% and 15b, 40 diameters; figs. 

 4, 5, 6, 7, 8, 9, 200 diameters; figs. 10, 11, 12, 13, 

 100 diameters. 



Fig. 1. A single hydra. a the stem; ( the coronal 

 tentacles. 



Fig. 2. A profile view of the upper part of an indi- 

 vidual, loaded with medusa3-buds. a the stem ; u^ 

 the horny sheath ; b the top of the stem ; c the 

 base of the head ; d (P (P e medusa; ; t coronal ten- 

 tacles; P t° proboscidal tentacles. 



Fig. 2^. The proboscis of fig. 2. p the mouth; p' the 

 intervals of the exterior row (^-) of tentacles ; p' the 

 decurrent bases of ^ ; P inner row of tentacles. 



Fig. 3. A much older head than fig. 2, with the coronal 

 tentacles (() cut oflf near the base, a the stem; a' 



