EXPLANATION OF THE PLATES. 



(21) 



c d e Jt i k cells laid open, and exposing their 

 numerous transverse partitions ; / y mouths of cells 

 not opened by the section ; j transverse partition of 

 k ; I common bottom of i and /■ ; m bottom of /; 

 and c, and perhaps of others. j diameters. 



Fig. 1.5, 1.5^ Seriatopora subulata. 



Fig. 15. Tip of a branch, a h c d e f g h i the cells ; 

 / and i the quadruple aperture of the cell ; k the pro- 

 jection of the central column, from which four par- 

 titions radiate to the walls of the cell. 40 diameters. 



Fig. 15*. Longitudinal section of a cell of fig. 15, one 

 inch from the top of tlie Ijranch. a mouth and h 

 bottom of the cell ; c axial column ; d e the four 

 cavities around the column ; / r/ transverse partition ; 

 h i solid part of the coral ; j bottom of the upper- 

 most cell. 40 diameters. 



TABLE XVI. 

 IIydractini.a. i'Olyclix.\ Aff. 



[Figs. 1, la, lb, Ic, Id, le, 2, 2a, 21), 2c, 2e, 4a, 4b, are drawn from 

 nature hy A. Soarel; the otliers by 11. J. Clark.] 



Fig. 1. A female hydromedusarium. A B C F fertile 

 individuals ; I) E G II I sterile individuals ; K basal 

 or stolonic layer ; e medusa ; Ji head of fertile individ- 

 uals ; p proboscis ; s spiny, horn-like processes from 

 the base. 25 diameters. 



Figs. I'', lb, ic, idj je^ different attitudes of the proboscis 

 and tentacles which the sterile heads assume. Hi the 

 mouth or actinostome; t the tentacles. 100 diameters. 



Fig. If. Profile of a sterile female strongly contracted. 

 m mouth; t tentacles. 60 diameters. 



Fig. 18. A fertile female hydi-a without any medusa;, t 

 tentacles. 100 diameters. 



Fig. i. A male hydromedusarium. A B C K the fer- 

 tile individuals; D E F G H I sterile individuals; 

 letters as in fig. 1. 25 diameters. 



Fig. 2». A fertile male with the proboscis expanded 

 and the mouth (m) wide open. t the globular ten- 

 tacles. 100 diameters. 



Fig. 2''. The same as fig. 2a with the mouth (;h) shut. 



Fig. 2''. A sterile male strongly contracted, so that the 

 tops of the tentacles are globular, and in two rows 

 (( t°). 100 diameters. 



Fig. 2<'. The tentacles more strongly contracted than 

 in fig. 2<^ ; the proboscis reverted and the mouth 

 wide open. 125 diameters. 



Fig. 2"^. The same as fig. 2*', but the proboscis (p) 

 more enlarged. 



Fig. 



A globular tentacle of a fertile male, a outer 

 and h inner wall ; d prolongation of the digestive 

 cavity. 500 diameters. 



A sterile male strongly contracted, p probo-s- 

 cis; t tentacles. GO diameters. 



2^. The proboscis of a sterile male, a outer and 

 h inner wall; d digestive cavity; m mouth. 300 

 diameters. 



■. 3. A fertile female crowded with medusae. a 

 outer and h inner wall ; a' outer and ?;' inner wall 

 of the medusa; c peduncle of the medusa; d diges- 

 tive cavity; iP digestive cavity of the proboscis of 

 the medusa ; e eggs ; p proboscis of the medusa ; t 

 tentacles; A a medusa foreshortened. 300 diameters. 

 ;. 3^ View from the actinal end of a medusa of 

 fig. 3. ((' outer and i' inner wall ; v yolk sac ; y 

 yolk ; p Purkinjean vesicle ; «• Wagnerian vesicle ; 

 vl Yalentinian vesicle ; A one of the eggs in a 

 superficial view. 500 diameters. 



;. 4. A fertile male crowded with medusa?, which 

 are discharging their spermatic particles, u partially 

 empty and b entirely empty medusa; ; /( the head. 

 1 25 diametei's. 



. 4". Actinal end of a fertile male hydra, a to i 

 difierent stages of development of the medusa? ; m 

 the open mouth. 100 diameters. 

 . 41). Similar to fig. 4», but younger, h the head. 

 . 5. A young sterile male and a jjortion of the 

 retiform stolon. a outer wall of the stolon ; a} outer 

 wall of tlie hydra ; l> network formed by the interior 

 wall; c digestive cavity; d inner wall; e and / 

 horn-like' spines; ^ proboscis; t tentacles. 300 diams. 

 5*. A portion of the edge of a stolonic base to 

 show a budding of a new channel (f) ; c outer 

 wall; a h line of the section from which fig. So was 

 taken ; d cells of the outer waU ; e chymiierous canal ; 

 /' yoinig canal budding ; g gi'anular contents of e. 

 400 diameters. 



;. 5'>. A very young male hydra budding from the 

 base. a outer and h inner wall of the stolon ; a' 

 outer and V- inner wall of the hydra ; c digestive 

 cavity. 400 diameters. 



;. 5'^. A section through a b, fig. !i\ a n' outer 

 wall ; b cells in a a''; c chymiferous canal of the inner 

 wall (</). 



■. (5. One of the horn-hke spines of fig. 5, to show 

 that it is covered by the retiform stolon, a inter- 

 stices of the net-work : b i' the canals ; c the spinules 

 of the spine ; d outer wall. 300 diameters. 

 ;. 7. A very young male medusa bud. a outer 



