HYDROZOA. 
525 
10. Hackel, E. Ueber eine sechszahlige fossile Rhizostomen uud eiiie 
vierzahlige fossile Semiostomen. Jen. Z. Nat. viii. pp. 308-330, pis. 
X. & xi. 
11. Mrtsciinikopf, E. Studien iiber die Entwickelung der Medusen 
und Siphonophoren. Z. wiss. Zool. xxiv. pp. 15-83. 
12. Plessis, Gr. DU. Sur un cas de double generation alternante chez la 
Campanularia {Clytia) voluhilis. Bull. Soc. Vaud. xii. pp. 429-435 ; 
abstract, R. Z. (3) ii. pp. xii. 
F. E. Schulze has published a note, “Ueber das Praparieren vonQuallen 
und Hjdroidpolypen,” in Arch. Ver. Mecklenb. xxv. pp. 107 & 108. 
Embryology, Anatomy, and Physiology. 
Van Beneden’s investigation of the place of development of the gener- 
ative products in Hy dr actinia has led to the important discovery that 
the male element is developed from the ectoderm, the female from the 
endoderm. The “ sporosacs ” or gone phores are developed only from a 
special region of the gonosome, situated above the gastric region ; in this 
region, the immature eggs — which are at this stage only large flagellate 
endodermal cells, with nuclei of a size much exceeding that of the 
ordinary endodermal cells — are discernible in the young gonosomes of 
the female colonies, at a time when the gonophores themselves have not 
begun to make their appearance as conical projections from the germi- 
native region of the gonosome. But, in the female gonophores, is also 
developed, through a sort of invagination of the ectoderm, a rudimentary 
sperm-sac, which may be observed in the mature gonophore as a thin 
pellicle outside of the eggs, while in the male gonophores this same 
organ is fully developed and filled with spermatozoa. As far as, in the 
germinative region of the male gonosomes, endodermal cells are dis- 
cernible, distinguished by nuclei of extraordinary size, and therefore 
comparable to the embryonic ova of the female gonosomes, a rudi- 
mentary ovary may also be said to be present in the male gonosomes. 
Generalizing from this discovery, the author considers the outer (animal) 
germ-loaf as being the male, and the inner (vegetative) germ-leaf as 
being the female, element in the composition of the embryo of higher 
animals. In addition, the recent histological discoveries in the Hydrozoa 
are confirmed for the Hydractinia ; the ectodermal and endodermal cell- 
layers are separated by a structureless membrane, to the outer side of 
which the muscular fibrils, which are in continuation with the ecto -7 
dermal cells, are fixed, &c. The gonosomes are not absolutely without 
mouth, a narrow orifice being left ; rudimentary tentacles are present, in 
the shape of tubercles containing thread-cells. 
Metschnikofp has confirmed (11, pp. 17-27, pis. ii. & iii.), from con- 
tinuous observations, the direct development from the egg, without any 
intervening gemmiparous hydroid generation, of certain lower Meduaa', 
{Genyonia [Carmarina'] hastata, Polyxenia leucostyla^ W., = JEgineta 
flavcscens, G., uEginopsis mediterranean Miill). The buds of Cunina rlio- 
dodactylaj H., are found free in the stomach of the mother ; when the 
