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 
Ooryne 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 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 
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; &, "jelly;" c, ectoderm. 
Fig. 8. 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. 6. Sperm-sac of Hydra viridis : a, 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 tJie 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 vertebrse, 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 tlie spinal canal. The 
