(20) 



EXrLAXATIOX OF THE TLATES. 



Fig?. 1. l!>, aiul 2. IVmiaria gibliosa. 

 Fiir. 1. A bi-oadsiilc view (if a stem, natural size. a 

 the stem : b tlio large teniiiiial livih-a- of the branelies 

 ((■) ; <l the lai-ge tenuinal hvtlra of the stem. 

 Fig. l;i. View at right angles to fig. 1, to show the 



curve of the stem and branches. 

 Fig. i. A portion of the stem, bearing a braiieh. A 

 the main stem: A' rings of A: B the large terminal 

 hyilra of the branch : C the youngest hydra, a mere 

 bud as yet ; 1) E F (! hydne. lettered according to 

 their ages; a basal rings of the branch: «' rings along 

 the branch; o° terminal rings of the branch; a^ pe- 

 dicel of C; (I* end of the pedicel of D ; h pedicel 

 of the large meilusa QP) of G ; d the medusa of D ; 

 <?' medusa of E : ip tP medusa- of F ; iP d* medusse 

 of G : (• t' the sexual oi-gans of the medusa (</') ; 

 c' circular canal of iP ; /" the proboscis of iP ; (/ the 

 tentacles of tP ; h the radiating canals of cP ; »i mouth 

 of the hydra : j' proboscis of the hydra ; /<' the bulging 

 side of p : ]>' the proboscis of F, stretched out : / P 

 the crown of tapering tentacles: (' (- the globe-tipped 

 tentacles of the proboscis. l-') diameters. 

 Figs. 3 to 13. ^lillepora alcicornis. 

 Fig. 3. A branch, natural size, covered by the extruded 



hydra\ 

 Fig. 4. A portion of fig. 3. magnified, a the outer wall 

 in profile ; b the surface of the branch ; c <; !i the 

 larger forms of hydra>, ■with only four to six tenta- 

 cles ; ill m n the smaller hydra-, witli numerous 

 tentacles: i! the mouth of c, shown liy the bending 

 of the head to one side; c the aperture of the cell 

 of (■ ; /■ aperture of the cell of </ ; p aperture of the 

 cell of a small hydra. '2i diameters. 

 Fig. ."). One of the smaller hydra- of fig. 4. a the 

 outer and b the inner wall ; c c' digestive cavity ; 

 </ mouth ; e f g h i I: I in the short, globe-tipped 

 tentacles ; /; the groups of brown cells (fig. ij'^) in 

 the inner wall. 100 diameters. 

 Fig. .5^. A lasso-cell from the tentacles. (7 the empty 

 cell: b the base of the thread (d c /); c the thickened 

 portion. 500 diameters. 

 Fig. jb. A B C D E F other forms of lasso-cells, a 

 the cell ; b the base of the thread (iu A the barbs) ; c 

 the thread. 

 Fig. y. a b c brown cells from the inner wall. JOO 



diameters. 

 Fig. C. One of the larger hydra- of fig. 4, with four 

 tentacles. Letters as in fig. 5 excepting Ji. the stem 

 of the tentacle. 100 diameters. 

 Fill. 7. Sectional view of fig. G, to show the form of 



the cells of the inner wall. Letters as iu fig. ;>. 100 

 diametei-s. 

 F\<z- S. -\ jiortion of the surface of a branch, to show 

 the form of the cells, a aperture of a cell of a large 

 h\dra ; b cell ot' a small hydra ; c the soft walls of 

 the hydro-medusarium through which the calcareous, 

 spongiform coral shines ; d the spongiform body of the 

 coral denuded ; c f views into the cells of the large 

 hydra- ; (] if cells of small hydra- ; li i j l irregular 

 radiating partitions of the cells of small hydra- ; / m 

 radiating partitions of a large cell (c). 100 diame- 

 tei-s. 



Fig. ?. Longitudinal section of the cell of a large hydra 

 with three transverse partitions, taken at a point one 

 half of an inch below the tip of the branch. ir the 

 uiouth of the cell : // the bottom of the cell : c trans- 

 vei-se partitions; <l irregular projections t'roni the bot- 

 tom of the cell : t apertures in the side of the cell, 

 leading off into the spongiform mass : /' branching 

 cavities in the coral ; (/ h sections of cavities like ( . 

 loo diameters. 



Fig. 10. Longitudinal section of a young, large hydra, 

 taken at a point half an inch below the tip of a 

 young branch, a mouth of the cell : b bottom of the 

 cell: [■ sides of the cell: (/ cf radiating partitions; 

 (/ section of an aperture like /( : / J branching ca-vi- 

 ties iu the coral; I: solid part of the coral. UiO 

 diameters. 



FiiT. 11. Transverse section of a branch one inch be- 

 low its top. (( highly spongiform axis; b mouth and 

 c bottom of the cell ; (/ t' k transverse partitions ; 

 e f g li i cells more or less exposed ; / surface of the 

 branch. 40 diametei's. 



Fit;. Vl. Transverse section one eighth of an inch be- 

 low the top of a branch. a the spongiform axis; 

 b d e f cells in various stages of develojiment ; c g 

 bottom of the cells. 40 diameters. 



Fig. 13. Longitudinal section of a large cell, ti-om a 

 stem half an inch in diameter. a mouth and b 

 bottom of the cell; c the numerous transverse par- 

 titions; d the upper part of the cell oidy p;u-tially 

 liud open. 40 diameters. 



Fie. 14, 14!', 14I). Pocillopora damicornis. 



Fij. 14. The tip of a young branch. a the young- 

 est, and b c d e J g successively older cells. 40 

 iliameters. 



Fie. 14*. Transvei-se section of two young cells, a h, 

 from fig, 14; </ and e the bottom of the cells; c c' 

 ridges between the cells. 



Fie, U''. Loneitudinal section of an old branch, a h 



