EXPLANATION OF THE PLATES. 



(11) 



of which p is the Piirkinjean vesicle ; w the Wag- 

 nerian vesicle ; y the yolk ; v the vitelline sac, 400 

 diameters ; C the Purkinjean vesicle {p), seen iso- 

 lately ; «' Wagnerian vesicle. 500 diameters. 



Fig. 17. A pair of young hydra^, a little younger than 

 fig. (S, with the same lettering. 300 diameters. 



Fig. 18. The horn-like sheath of fig. 6. a b c the parti- 

 tion between the hydra; and the main stem. 150 diams. 



PLATE XXXIII. 



Obelia commissuralis McCr. 

 [Figs. 1 and 2, drawn by A. Sonrel; the others by H. J. Chirk.] 



Fig. 1. A hydrarium, full grown, and natural size. 



Fig. 2. A hydromedusarium, attached to a sea-weed. 

 Natural size. 



Fig. 3. A growing branch and pedicel. a the outer, 

 and /3 the inner wall of the branch ; y the processes 

 from the outer wall ; f the rings of the horn-like 

 sheath ; o' the outer, and ?/' the inner walls of the 

 young pedicel ; c" the horn-like film over n' ; </' the 

 end of the chymiferous channel. 500 diameters. 



Fig. 3*. The main stem, from which a branch is begin- 

 ning to bud. a /3 7 as in fig. 3 ; (i the upper edge 

 of the bud, overlapping the outer wall (f) of the 

 stem ; a' outer, and V inner wall of the bud ; t" the 

 old horn-like sheath, thrown off by the expanding 

 bud ; c' the new sheath of the bud. 500 diameters. 



Fig. 4. A half-developed hydra, n outer, and b inner 

 wall of the head ; «' outer, and 6' inner wall of the 

 pedicel ; c^ cavity of the calycle ; e- uppermost ring 

 of the pedicel ; c' the calycle ; g the digestive cavity. 

 500 diameters. 



Fig. V^. An end view of the polygonal cells of the 

 outer wall (a) of fig. 4. 500 diameters. 



Fig. 5. A sectional view of an adult hydra, a outer, 

 and b inner wall of the head ; «' outer and i' inner 

 wall of the pedicel ; a- outer, and h° inner wall of 

 the tentacles ; a' outer, and V inner wall of the 

 proboscis ; c' cavity of the calycle (c') ; c' rings of 

 the pedicel ; rj the digestive cavity ; if cavity of the 

 proboscis {pr) ; t tentacles. 200 diameters. 



Fig. oil. Looking into the mouth (;«) of the proboscis 

 of fig. 5. 



Fig. 5b. A tentacle of fig. 5. a? and J- as before ; 

 I lasso-cells ; a an infusorium, encircled by lasso-threads. 

 500 diameters. 



Fig. 6. A portion of the branch of a hydromedusarium. 



(i the branch ; y the top of /3 ; 6 the branchlct ; e 

 rings of the horn-like sheath ; f rings of the pedicel 

 of 15 ; 15 the hydromedusa ; C C hydrse ; C^ the 

 rings of the pedicel of C. fiO diameters. 



Fig. 7. A hydra, with budding tentacles. Letters as 

 in fig. 5 ; also c the point of attachment to the 

 semi-partition. 60 diameters. 



Fig. 7". The end of a tentacle of fig. 7. 500 diams. 



Fig. 8. A young hydra, just upon the point of emerg- 

 ing from the calycle. c the attachment to the semi- 

 partition ; c* the sides, and c' the angles of the 

 polyhedral aperture of the calycle ; d the opercle ; 

 rf' the inrtected edge of rf; t tentacles. 125 diams. 



Fig. 9. A hydra a little older than fig. 7. 125 diams. 



Fig. 10. A hydra similar to fig. 8. d the opercle 

 depressed. 1 25 diameters. 



Fig. 11. A branch of a hydromedusarium. A B the 

 reproductive hydrje ; C the hydnc. 1 1 diameters. 



Fig. 12. The calycle of a hydra in profile. c the 

 semi-partition ; c' the cavity of the calycle (c) ; c~ the 

 pedicel ; t' the sides, and c' the corners of the poly- 

 hedral aperture. 300 diameters. 



Fig. 12'>'. The same as fig. 12, looking into it; c c' 

 c^ c' as before. 



Fig. 13. A portion of the pedicel of a hydra, beset 

 with lasso-cells («') ; c' the concentric layers of the 

 horn-like pedicellar sheath. 500 diameters. 



Fig. 14. A portion of the main stem in a state of 

 decomposition. o' inner, and 6' outer wall ; e" the 

 lamellated, horn-like sheath. 500 diameters. 



PLATE XXXIV. 



Figs. l-9a. EucoPE DiAPHANA A(j.\ Figs. 10-21, Obelia 



COMMISSURALIS McCr. 



[Figs. 4 and 9, drawn by A. Sonrel; the others by H. J. Clark.] 



Fig. 1. A portion of the stem of a hydrarium. « o' 

 «- a profile of the concentric laminas ; b the inner 

 face exposed ; c loosened filaments or shreds. 400 

 diameters. 



Fig. 2. The calycle and its pedicel, obliquely in profile. 

 a o' the thick wall of the calycle ; e c' the thickness 

 of the stem ; / the basal attachment of the joint 

 above ; (j-h one joint of the stem ; k the semi-par- 

 tition. 100 diameters. 



Fig. 3. A hydra with partially contracted tentacles (b i'). 

 a the calycle ; d the proboscis. 1 25 diameters. 



Fig, 4. A birds-eye view of a hydra ; 6 rf as in fig. 3. 



