Observations on British Zoophytes. 221 



tact with the generative elements, is transparent and struc- 

 tureless. 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 

 Hydracttnia, 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 endo- 

 derm, which continues to convey nutriment to the former 

 until they are fully developed. 



EXPLANATION OF PLATE IX. 



Fig. 1. Male organs of Chrysaora hyoscella : a, grape-like bodies dotted with 

 eperni-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; b, "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 spermatic 



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

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



spermatic cells ; c, spermatozoa bearing the same relations to the 



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



III. On the Serial Homologies of the Articular Surfaces of the Mam- 

 malian Axis, Atlas, and Occipital Bone. By John Cleland, M.D., 

 Demonstrator of Anatomy in the University of Edinburgh. 



In works on human anatomy it has been customary to 

 compare the articular surfaces of the atlas, and the superior 

 articular surfaces of the axis, with those of the oblique pro- 

 cesses of other vertebrae, as if they were homologous, not- 

 withstanding the apparently anomalous manner in which, 

 according to that view, the first and second spinal nerves 

 must be considered as emerging from the spinal canal. The 



