ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 201 



of all the rhopalia usually ceased to pulsate. The pulsation centre is 

 between the eye part and the stalk of therhopalium. The nerve plexus 

 is probably absent in the upper third of the bell and in the region near 

 the velarium. The phacellse are nine to ten in number in each inter- 

 radial corner of the gastral cavity. They are not dendritic. Each 

 consists of a very elastic stalk and a terminal tuft. 



Nerve Conduction in Cassiopea.* — A. G. Mayer finds that the rate 

 of nerve conduction in this Medusa may be independent of the electrical 

 conductivity of the solution surrounding the nerve, but is proportional 

 to the concentration of the sodium, calcium, and potassium cations in 

 the sea-water. R. S. Lillie is right in stating that the rate of nerve 

 conduction in Cassiopea in diluted sea-water does not decline in accord 

 with Freundlich's law of adsorption, 



Porifera. 



Larva of Horse-sponge.t — C. Vaney and A. Allemand-Martin discuss 

 the larval development of Hippospongia equina on the Tunis coast. The 

 larvae escape from the oscula between the end of March and the third 

 week in June. They are covered with short cilia, except on a limited 

 pigmented ring posteriorly, where there are very long locomotor flagella. 

 They seek shade, but not darkness. They are very sensitive to changes 

 in salinity. The whole surface is covered with minute cylindrical 

 epithelial cells. Beneath these is a zone of crowded nuclei. The rest of 

 the body consists of cells mostly fusiform and a number of muscular and 

 elastic fibrils. There is no cavity. 



Buds of Donatia.l — Blanche B. Crozier has studied Bermudian 

 species of Donatia {Tethya) and their budding. In D. seycheUensis a 

 typical full-grown bud is spherical or egg-shaped, 2-5 mm. in diameter, 

 of a bright clear orange colour, borne on a stalk projecting on the 

 distal side. They contain, like the body of the sponge, megascleres of 

 the Strongyloxea type, spherasters, oxyasters, and chiasters. The buds 

 drop off and settle on the bottom. A description is also given of two 

 varieties of D. ingalli and D. lyncurium. 



Desmacidonid Sponges.§ — E. F. Hallraann defines, with much detail 

 as regard the siliceous spicules, the genera Echinaxia and Rhabdosigma, 

 with remarks on their probable relationships, and re-descriptions of their 

 type-species. 



Protozoa. 



New Genus of Heliozoa.|| — Clifford Dobell describes Oxnerella 

 maritima g. et sp. n., an Aphrothoracan Heliozoon of very small size 

 (10 /x to 22 fji in diameter). It is a solitary form, free-floating or 



* Proc. Nat. Acad. Sci. U.S.A., ii. (1916) pp. 721-6. 



t Comptes Rendus, clxvi. (1918) pp. 82-4. 



I Ann. and Mag. Nat. Hist., i. set. 9, pp. 11-18. 



§ Proc. Linn. Soc, xlii. (1917) pp. 391-405 (2 pis. and 2 figs.). 



U Quart. Journ. Micr. Sci., Ixii. (1917) pp. 515-3S (1 pi.). 



