(8) 



EXPLANATION OF THE PLATES, 



Fig. 1. A male hydromcdusai-ium attached to a sea- 

 weed. Natural size. 

 Fig. 2. A portion of fig. 1. a the pedicels of the 

 hydrse; h the reproductive calycles; c c' the young 

 hydra-buds; d the stolon. 15 diameters. 

 Fig. 3. A sectional view of a hydra pedicel (f') and 

 head. a outer, and h inner wall of the head; c the 

 semi-partition ; c' cavity of the calycle ; c- pedicel ; 

 c' top of e^; c* the stolon; (j digestive cavity; t 

 two opposite tentacles. 

 Figs. 4, 5, 6, 7, 8, 9. Progressive stages in the develop- 

 ment of the hydra. a the outer, and h the inner 

 wall of the head; a' outer, and i' inner wall of the 

 pedicel ; ah the tentacular region ; c the semi-par- 

 tition ; c' cavity of the calycle ; c- chitinous sheath ; 

 (/ the opercle ; e point where the walls adhere to the 

 calycle ; g digestive cavity. 

 Fig. 10. A hydra just emerging from its embryonic state. 



d the opercle ; t the tentacles. 

 Fig. 11. The bud of a fertile male hydra. /3 outer, 

 and y the inner wall ; b chymiferous cavity ; d the 

 growing terminus ; i a medusa-bud ; k the calycle. 

 Fig. 12. The same as fig. 11, but much further ad- 

 vanced. The letters the same : also a, the chymi- 

 ferous cavity. 

 Fig. 13. A male reproductive hydra. a the single 

 chymiferous channel ; c c^ c' the multiple chymiferous 

 channels ; d the common terminal cavity ; / radiating 

 tubes of the medusa ; i the spermatic mass. 

 Fig. ISi". The hydromedusa of fig. 13, taken from its 

 calycle, and allowed to exjiand so as to show the 

 point of connection (e') of the medusa to one chan- 

 nel of the multiple axis. 

 Fig. 14. A two thirds grown hydromedusa, removed 

 from its calycle. a base of the channel of c ; h 

 junction of the medusa with a ; c channel of the 

 axis ; d expanded terminus of c ; / radiating canals ; 

 i spermatic mass. 

 Fig. 15. A female hydromedusa. o the main channel; 

 h neck of the medusa ; c c' e^ c' c' the multiple chan- 

 nels arising from a ; d common cavity into which c- 

 c' empty ; e e' /' /' radiating tubes of the medusa ; 

 h actiual side of the medusa; i i' the plauulie; Ic l^ 

 the calycle. 

 Fig. IG. A mature female hydromedusa. a h c c^ c° d 

 e e^ f i ? k k'^ as in fig. 15; c' radiating tube; li a 

 portion of the medusa protruded from the calycle ; 

 A' neck of h ; r planula;. 

 Figs. 1 7 and 1 7^. A lateral and end view of a planuloid 

 hydra from fig. 15. 



Fig. 18. A the outer cells of fig. 17; B the interior 



cells of the same. 

 Fig. 19. A male hydromedusa, two thirds grown, a b 



c c^ d e e' e^ //' k as in fig. 15; also i, the spermatic 



mass. 

 Fig. 20. B, spermatic particles; A, a diagrammic figure 



of A ; C, immature spermatic particle. 



PLATE XXIX. 



Figs. 1-5, Clytia poterium Ag.; figs. 6-9 C. Bico- 

 PHORA Ag.; Figs. 10 and 11, C. intermedia Ag. 



[Drawn by H. J. Clark.] 



Fig. 1. A hydra which has developed from the head 

 of another hydra. a the base of (a') the pedicel of 

 the upper hydra; a' the semi-partition; b the terminal 

 ring of the lower pedicel; b" terminal ring of the 

 upper pedicel. 100 diameters. 



Fig. 2. A male hydromedusa. a main chymiferous chan- 

 nel ; b base of the multiple channels (c' c- c') ; c' c^ 

 outer wall of the hydra ; d common chymiferous cavity ; 

 e e' e- radiating tubes of the medusa; / branches of e; 

 (/ (/' fun-ow in the spermatic mass. 150 diameters. 



Fig. 3. A mature male hydromedusa. Letters as in fig. 2 ; 

 also (, the spermatic mass. 100 diameters. 



Fig. 4. Similar to fig. 3, and with the same letters. 



Fior. 5. A mature male hydromedusa, discharging its 

 spermatic particles, the multiple axis partially retracted. 

 a main channel ; b base of the multiple channels (c c' c") ; 

 d end of the axis; h the medusa; i i' the current 

 of spermatic particles ; k the calycle ; k^ the mouth 

 of k. 100 diameters. 



Fig. 6. A hydromedusarium of Clytia bieophora. A-G 

 the hydra ; a h c f the base of the branch of a hydra ; 

 d e the reproductive hydra ; g the stolonic sheath ; h 

 the channel of the stolon. 40 diameters. 



Fig. 7. A hydra from fig. 6. c the semi-partition ; c- 

 the terminal ring of the pedicel ; c' the teeth ; t' the 

 sinuses between c". 100 diameters. 



Fior. 7a. End view of fig. 7, with the same letters. 



Fio-. T''. A portion of the calycle of fig. 7, with the 

 same letters. 100 diameters. 



Fio-. 8. The calycle of an immature hydra, b the ter- 

 minal ring of the stem; c the semi-partition; d the 

 filmy opercule. 200 diameters. 



Fif. 9. The margin of the calycle of a mature hydra 

 just before it emerges, c' c' e'= the teeth; c^ the de- 

 current angles of the intervals (c') of the teeth c°) ; 

 d the opercule ; rf' line which divides the smooth from 



