236 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Occasionally indubitablo ogg-cells aro to be found in the endoderm. 

 The sexual cells of the Cladoncruidaa appear to be developed, in all 

 cases, in the endoderm. If the continuation of tho author's studies 

 shall confirm this generalization, we have here a further point of agree- 

 ment with the Ctenophora. 



Hydra.* — Prof. J. Leidy thinks that Prof. L. Agassiz was wrong 

 in naming the two American species of Hydra, H. gracilis and H. carnea, 

 as they do not scorn to bo really distinct from tho European H. viridis 

 and II. fusca. 



Are there Deep-Sea Medusae?! — ^ r - J- "W. Fewkcs discusses the 

 difficult question of tho bathymetrical distribution of Medusao. He 

 notes (1) the two wholesale methods of dredging, which leavo the actual 

 depth of habitat often very hypothetical, tho negativo results as yet 

 obtained by tho use of a contrivance like Sigsbeo's " gravitating trap," 

 and tho unsatisfactoriness of actual records. (2) He approaches the 

 subject from another side, and suggests the study of characteristics of 

 structuro in relation to probable environment. In illustration of this, 

 tho Siphonophore genus Bhizophysa, and the Acraspedan Collaspidao 

 (Atolla, Collaspis, Nauphantopsis), are discussed. These three last 

 genera present us the strongest arguments which can be found in the 

 modification of external and internal anatomy, as indicative of a deep- 

 sea habitat. In tho same way ho draws conclusions from Lucernarida. 

 But Mr. Fewkes is forced to confess that neither the data so far 

 gathered, nor the recorded depths, nor the structuro of tho genera 

 considered, demonstrate that there is a serial distribution of free medusas 

 in bathymetrical zones. For all that he concludes that the case for the 

 affirmative is stronger than the arguments suggest. 



Sex-cells and Development of Millepora.J — Mr. S. J. Hickson 

 communicates his observations on the sexual cells and the early stages 

 of development of Millepora plicata found abundantly on the fringing 

 reefs of Talisse Island, N. Celebes, (a) The young sex-cells arise in 

 ectoderm of ccenosarcal canals, perforate the mesoglcea, and enter the 

 endoderm. The ovum is moored to the mesoglcea by a pseudopodial 

 stalk, or may withdraw this and migrate, (b) Before maturation the 

 germinal vesicle disappears, a longitudinally striated spindle-shaped 

 body appears, and gives off the first polar globule. A second does like- 

 wise. The mature ova, with yolk-globules or granules, measure only 

 1/100 mm. in diameter, (c) Two or three sperm-heads may be seen 

 within one ovum, the flagella stuck at the surface. The nucleus is 

 again visible after fertilization, subsequently with a number of nucleoli, 

 (d) The nucleus fragments, the portions are scattered in the pole nearest 

 stalk ; they travel to form an equatorial zone in middle of ovum ; the 

 zone divides, and the halves, with their fragments increasing in number, 

 size, and distribution, move towards the poles. The result corresponds 

 to a morula ; faint markings indicate cell-outlines, (e) As a solid blasto- 

 sphere, the embryo migrates into gastrozooid, and probably passes out 

 by mouth. There was no trace of medusa, medusiform gonophore, or 

 sporosac. 



The young male cells or spermospores have a large nucleus witli 



* Proc. Acad. Nat. Sci. Philad., 1887, pp. 311-3. 

 t Amer. Jourii. Sci., xxxv. (1888) pp. 166-7H. 

 X Proc. Roy. Soc, xliii. (1SS7) pp. 245-7. 



