16) 



EXPLANATION OF THE PLATES. 



the horny sheath ; a" the expansion of the sheath at 

 the base of the head ; </ (P tlie medusa; ; (' t" the 

 inner and outer rows of proboscidal tentacles. 



Fig. 4. A young medusa-bud, just rising from the disk 

 of the hydra. a outer, and i inner wall ; d chy- 

 miferous cavity. 



Fig. .5. A medusa-bud from the hydra disk. a outer, 

 and b inner wall ; c c' radiating tubes ; d digestive cavity. 



Fig. G. A medusa-bud from the hydra disk, already one- 

 sided, a 6 c c' rf as in fig. 5 ; c- the incipient tentacle. 



Fig. 7. A little older than fig. C, but from the base of 

 the tentacle of figs. 14 and 1 4^1. a h c c' c" as in 

 fig. C ; U inner wall of c". 



Fig. 8. A little older than fig. 7. From the hydra. 

 The letters the same ; ft- an incipient primary medusa. 



Fig. 9. Considerably older than fig. 8. From the hy- 

 dra, a b b- c c' c' d as before ; «' horny sheath ; 

 ft' a secondary medusa-bud ; (/' chymiferous cavity. 



Fig. 10. A medusa with four medusa-buds, a' b ft' ft', 

 c the tentacle. From the hydra. 



Fig. 11. A medusa in which the circular tube (ft") is 

 already developed. From the hydra, a outer, and 

 ft inner wall ; ft' the radiating tubes ; ft" circular tube ; 

 c the incipient bud of a secondary medusa; c- the 

 tentacle of c ; d outer, and rf' inner wall of the pro- 

 boscis ; d? digestive cavity ; e disk cavity ; //' second- 

 ary medusiE ; g tentacle of the primary medusa. 



Fig. 12. A medusa nearly ready to break loose from 

 the hydra, a outer, and 6 inner wall; ft junction 

 of radiating (ft' ft» ft") and circular (ft=) canals; ft' 

 hollow base of the tentacle {g") ; c a primary medusa ; 

 c' a secondary, and c° a tertiary medusa; d digestive 

 cavity; </' proboscis; e disk cavity; f an incipient 

 group of medusa; ; g g^ tentacle of c ; g° tentacle of 

 tlie parent medusa. 



Fig. 13. A medusa a little older than firr. 12: lookino- 

 toward the inner face of the tentacle. The letters 

 as in the last : also /' f- h the same as /in fig. 12; 

 i a primary medusa, a little younger than c ; i' p sec- 

 ondary arul tertiary medusa; of i; cf tentacle oft. 



Fig. 14. A medusa just set free, seen with the tentacle 

 in profile. 6 the radiating canal; ft- circular canal; 

 6* the hollow base of jr ; fts the canal opposite the 

 tentacle {g)\ d' the proboscis; (p the remains of the 

 pcdicellar attachment; /- medusa!-buds ; g the tenta- 

 cle ; I aperture of the veil (/•) ; » the prolonged edge 

 of the disk. 

 Fig. 14a. View of fig. 14, from the side opposite to the 

 tentacle, and obliquely from below. Letters as in fig. 

 14 ; also (/, the digestive ca-(ity. 



Fig. lo. A medusa, drawn about twenty-four hours after 

 it dropped from the hydra: the tentacle next the 

 observer. The letters as in figs. 14 and 14^ : also 

 y the solid part of the tentacle ; k the pair of pig- 

 ment bands on each side of the odd radiating canal; 

 i' base of k ; 1^ base of the other bands (k'). 



Fig. 15». View from above of fig. 15, with the same 

 letters. Also /.*, the ends of the pair of pigment- 

 bands. 



Fig. la*". The proboscis of fig. 1.5, elongated, a outer, 

 and ft inner wall; c mouth; d the base. 



PLATE XXVI. 



Figs. 1-G, TUBULARIA COUTHOUYI Ag. ; Figs. 7-17, 



CoEYMORPHA PENDULA Ag.; Fig. 18, Hydractinia 



POLYCLIXA Ag. 



[Figs. 1-5 anil 18, drawn by H. J. Clark; fig. 6 by .J. H. EicbanI; 

 figs. 7-17 by Wm. Tappan.] 



Fig. 1. A hydra just escaped from the parent, a the 

 stem ; ft the coronal tentacles ; c the buccal tentacles ; 

 (/ the base of ft. 100 diameters. 



Fig. 2. The same as fig. 1, in an expanded state, with 

 the same letters. 



Fig. 3. The medusa with the hydra of fig. 1, before it 

 escaped, a outer, and ft inner wall of the pedicel ; 

 c point of junction of the circular and radiating (e e') 

 tubes ; d the jtroboscis of the medusa, seen through 

 the hydra ( /"') ; «- base of e and e' ; _p tentacles of /'. 

 100 diameters. 



Fig. 4. .\ branch of withering medusa', a the branch : 

 b c d e the medusiE in various stages of decadence. 

 100 diameters. 



Fig. 5. A part of a medusiferous branch, to show the 

 relations of its walls to those of the medusa. a the 

 outer, and b the inner wall of the branch ; «' the 

 outer, and ft' the inner wall of the branchlot; c '■' 

 the chymiferous cavity; d the radiating tubes of the 

 medusa; e the proboscis. 60 diameters. 



Fig. 6. The hydrsi; a short time after birth, attached 

 to the stem of the parent (T). p the proboscis; s 

 the stem; .«' the base of s; t coronal tentacles. 40 

 diameters. 



Figs. 7 and 0-1 7. Hydromedusarium of C'oi-ymorpha, in 

 various attitudes. a the proboscis ; d the medusie. 

 Natural size. 



Fig. 8. A hydra, with the upper third of the stem very 

 much extended, and pendulous. a the proboscis; 6' 

 the base of the head ; A' the stem ; ft' the horn-like 



