in Chrysaora hyoscella. 359 



ganophthalmatous Medusre, Lucernarias, and Actinias, is thus 

 always formed of the endoderm or lining membrane of the diges- 

 tive system, while the sperm-sac of Hydra (fig. 5), the Hydroid 

 Polyps, and the Gymnophthalmatous Medusae is formed of the 

 ectoderm. In the first class of animals the spermatic cells 

 (fig. 4) become first matured into spermatozoa in the centre (c), 

 or at the base of the sperm-sac, the part most distant from the 

 endoderm (a). In the second class they ripen at the periphery, 

 or at the summit of the sperm-sac (fig. 5), the part also most 

 distant from the endoderm (a). 



My friend Mr. Hincks, in his valuable paper on Clavatella 

 contained in the February Number of this Journal, appears to 

 consider that the ova of that creature may be developed from 

 the ectoderm. But an examination of the embryology of a 

 very large number of zoophytes forbids me to entertain this 

 idea. The endoderm of the generative capsule in these crea- 

 tures consists of two layers intimately connected with each other. 

 The external layer, or that in contact with the generative ele- 

 ments, is transparent and structureless. The internal layer, 

 communicating with the cavity of the digestive system, is loaded 

 with brown granules. In Coryne glandulosa, the ova are at an 

 early period observed attached to the transparent layer of the 

 endoderm, and separated from the ectoderm by a wide space of 

 fluid. In Hydractinia, the reproductive polyps of which possess 

 a muscular coat, that coat intervenes between the ova and the 

 ectoderm. 



In the subject of this paper, the ectoderm does not enter at 

 all into the constitution of the sperm-sac. We may therefore 

 conclude that the ova and spermatic plasma are detached or 

 secreted from the external surface of the endoderm, which con- 

 tinues to convey nutriment to the former until they are fully 

 developed. 



EXPLANATION OF PLATE XVIIL 



Fig. \. Male organs of Chrysaora hyoscella : a, grape-like bodies dotted with 

 sperm-sacs and attached to the ovarian membrane, b; cc, tenta- 

 cular processes bearing tubercles and sperm-sacs. 



Fig. 2. Section of tubercle bearing sperm-sacs, from the extremity of long 

 oral tentacles : a, endoderm; 6, "jelly;" c, ectoderm. 



Fig. 3. Section of similar tubercle from Actinia mesembryanthemum, show- 

 ing sperm-sacs formed by and imbedded in endoderm, a ; b, in- 

 terstitial tissue. 



Fig. 4. Single sperm-sac of C. hyoscella : a, endoderm ; b, unripe sperm- 

 atic cells; c, spermatozoa; d, "jelly." 



Fig. 5. Sperm-sac of Hydra viridis : a, endoderm ; d, ectoderm ; b, un- 

 ripe spermatic cells ; c, spermatozoa bearing the same relations 

 to the constituents of the sperm-sac as in fig. 4. 



