312 SUMMARY OF CURRENT RESEARCHES RELATING TO 



migrates, along with the " clear spot " which forms the centre of the 

 sperm-radiation, towards the ovum-nucleus. It passes eventually into 

 one of the first two blastomeres, and is probably the bearer of a definite 

 protoplasmic idioplasm — a " plastochondrial mass." Perhaps those cells 

 which have no " middle piece " substance form those parts of the 

 Fluteus larva that come to nothing. 



Coelentera. 



Structure of Pteroides g-riseum.* — Albert Niedermeyer gives a 

 ■detailed account of the general and minute structure of this sea-pen. 

 In connexion with the canal system, he notes that the dorsal and ventral 

 main canals open separately by minute openings, and that there are no 

 others. The structure of the axis and its investment, and the muscula- 

 ture of the colony and of its members are fully discussed. An important 

 conclusion is that the siphonozooids do not differ in any essential respect 

 from the first stages of autozooids. The siphonozooids of the pinnules 

 are primitively simple, those of the rhachis are secondarily simple. An 

 account is given of the minute structure of the ectoderm, endoderm, 

 and mesog-loea. 



-'to' 



Axis of Plexaurids and Gorgonids.t — Hans Neumann has made 

 a minute study of the axis in various Gorgonacea, and finds that 

 von Koch's interpretation of the axis as the secreted product of an 

 ectodermic axis-epithelium cannot be sustained. The axis is not ecto- 

 dermic, but due to the mesoglcea, as is suggested by the frequent 

 presence of spicules in the cortex of the axis. Sometimes, moreover, 

 as in Phxaura fiavida, there is no axis-epithelium. In other cases the 

 axis-epithelium is clearly a differentiation of the mesoglcea. 



New Fresh-water Medusoid.| — C. L. Boulenger describes from 

 Southern Rhodesia (from a tributary of the Middle Zambesi), a new 

 species of Limnocnida, which he calls L. rhodesix. The umbrella has a 

 diameter of 6 mm. The " nettle-ring," instead of forming a broad 

 continuous band round the margin of the umbrella as in L. tanganicse, 

 is considerably narrower, and, moreover, discontinuous, the masses of 

 stinging cells being grouped round the bases of the tentacles, and 

 giving rise to distinct bulbous swellings similar to the tentacle bulbs 

 which have been described in many Trachymedusfe, such as Gonionemus 

 murhachi. 



Changes of Chromatin in Oogenesis of Hydrozoa.§ — J. Schaxel 

 deals first with the oogonia and oocytes of ^quorea discus. After 

 the last oogonial division the chromosomes become filamentous with 

 enchylema aggregated around them. A diffuse chromatin-emission leads 

 to the formation of extra-nuclear bodies. The chromosomes are then 

 re-integrated from the chromatin below the surface of the nucleus. 

 When the nucleus is dissolved, the nucleolus, which does not stand in 



• Arbeit. Zool. Inst. Univ. Wien, xix. (1911) pp. 99-164 (2 pis. and 8 figs.). 



t Jen. Zeitschr. Naturw., xlvii. (1911) pp. 497-528 (19 figs.). 



X Quart. Journ. ]\Iicr. Sci., Ivii. (1912) pp. 427-38 (1 pi. and 2 figs.). 



§ Zool. Jahrb., xxxi. (1911) pp. 613-56 (3 pis.). 



