(4) 



EXPLANATION OF THE PLATES. 



Fig. 17. The proboscis of fig. 12. a remains of the 



germ-basis; b wall of the proboscis ; c chymiferous cavity. 

 Fig. 17a. The same as fig. 17, contracted, and the germ- 

 basis wrinkled and having the appearance of an outer 



wall. 

 Fig. IS. A portion of a medusiferous branch, partially 



contracted, a outer, and b inner wall; c chymiferous 



channel. 

 Fi". 18a. The same as fig. 18, but uncontracted. 

 Fig. 19. The same as fig. 18, in a sectional view. 

 Fin. 19". The same as fig. 19, contracted. 

 By mistake there is no figure 20. 

 Fig. 21. A young hydroid, just beginning to develop 



its tentacles, b. a the inner mass or wall ; c outer wall. 

 Fig. 21". A portion of fig. 21. a inner wall; a' inner 



wall of the tentacle; b an incipient tentacle; c outer 



wall. 

 Fig. 22. A young hydroid with (juite prominent tenta- 

 cles (b). a inner, and c outer wall. 

 Fig. 22a. A portion of fig. 22. Letters as in fig. 21". 

 Fig. 23. A young hydroid with tentacles ■ already flexible. 



a inner wall ; a' h tentacles. 

 Fig. 23". A portion of fig. 23. Lettered as in fig. 22*. 



a} and a' axial cells of the tentacle. 

 Fig. 24. A portion of the young hydroid in fig. 11, e. 



a inner wall; c outer wall. 

 Fig. 25. A portion of fig. 21'', more highly magnified. 

 Fig. 26. The end of the tentacle of a hydroid, just 



issuing from the parent ; lateral view. a outer wall ; 



a} a^ lasso-cells in a ; b V inner wall ; c globular tip, 



crowded with lasso-cells. 

 Fig. 26". The same as fig. 26, but more extended ; seen 



from the actinal side. 

 Fig. 261'. The same as fig. 26*, but the lasso-cells more 



prominent. 



PLATE XXXma. 



Figs. 1-7, Parypha crocea Afj. ; Figs. 8 and 9, Tuiiu- 

 LARIA CouTHOUYi ^4^.; Figs. 10 and 11, IIyboco- 



DON PROLIFER Ag.\ Fig. 12, CoKYNE MIRABILIS .4^. 

 [Drawn from nature by H. .J. Clark.] 



Figs. 1, la, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, magnified 500 

 diameters; Fig. 8 magnified 40 diametei-s. 



Fig. 1. A lateral view of a coronal tentacle in a highlv 

 extended state. a a' a- cells of the outer wall, in 

 profile ; b b^ b- b' b* general view of the cells of the 

 outer wall, in outline; c c' <r c' superficial view of 



the outer wall, c' lasso-cells; d cells of the inner wall 

 or axis, seen through the outer wall ; e the same as 

 d, seen isolately. 



Fig. la. Cells from the disintegrated outer wall. a-d 

 lasso-cells; e granular contents. 



Fig. 2. View from below at the surface of the axis of 

 a coronal tentacle, a a' a' as in fig. 1 ; a' lasso- 

 cells; e the two rows of cells nearest the eye, which 

 meet along the line e'. 



Fig. 3. Transversely sectional view of fig. 1. a cells 

 of the actinal side ; o' cells of abactinal side ; or cor- 

 responds to a- in fig. 1 ; i' i' correspond to i' i' in 

 fig. 1 ; e e' same as in fig. 2. 



Fig. 4. A combined profile and general view of a por- 

 tion of the stem, just below the head. a the horny 

 sheath ; b c outer wall, in profile ; 6' lasso-cells ; d e 

 inner wall, in profile ; //' /' f f* inner wall in pro- 

 file, seen through the cells nearest the eye (g) ; g^ fi- 

 end view of the cells of the inner wall, seen through 

 those of the outer wall (f) ; k i ir ? general view of 

 the outer wall. 



Fig. 5. The stem of a young hydra, at the upper third, 

 stretched longitudinally. The lettering as in fig. 4 ; 

 in addition, g'' cells of the semi-partition, corresponding 

 to g' g* in fig. 7. 



Fig. 6. A cell of the outer wall of fig. 4. a lasso- 

 cell ; b c wall of the cell ; d cavity of the cell. 



Fig. 7. Transverse section of the stem, a little below 

 the head. The lettering as in fig. 5 ; in addition, J 

 is the loose pigment layer. 



Fig. 8. A transverse section of the stem of Tubularia 

 Couthouyi Ag. a horny sheath ; b outer wall ; d 

 inner wall; g' g* the solid cellular mass which fills 

 the axis of the stem; j the longitudinal channels; _;' 

 the primary channel. 



Fig. 9. A portion of fig. 8, more highly magnified, a 

 lamellate sheath ; b outer wall ; d d' inner wall ; g 

 cells of the solid central mass ; g^ mesoblast of the 

 cells (g) ; </" outline of cells like g, but in the dis- 

 tance ; g' mesoblast in profile. 



Fig. 10. A portion of the transverse section of the stem 

 of Hybocodon prolifer Ag. a the lamellate sheath ; 

 b bb outer wall ; d inner wall ; dd pigment cells ; g^ 

 g* the semi-partition. 



Fig. 11. Inner face of a semi-partition of fig. 10, with 

 the same letters, and y' a mesoblast. 



Fig. 12. A transverse section of the stem of Coryne 

 mirabilis Ag. a the horny sheath ; b c cells of the 

 outer wall ; i' a mesoblast ; d e cells of the inner 

 wall ; dd pigment cells. 



