474 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Marginal Glands of Porpita.*— A. Issakowitsch describes the trans- 

 formation of the epithelium of the "collar" into glandular cells. These 

 show very distinct chromidia, and the author makes it clear that the 

 chromidia play an essential part in the production of mucus. 



Mediterranean Species of Halecium.t — S. Motz-Kossowska, in her 

 survey of the Hydroids from the Western Mediterranean, deals with the 

 species of Halecium, describing two new forms — H. billardi and //. torreyi 

 — and giving some details in regards to others. 



Hydractinia and Hermit-crab.:}: — Seitaro Goto describes two species 

 of Hydractinia (H. sodalis Stimpson, and H. spiralis sp. n.), very 

 different in external appearance, which have the same habit of liviug 

 always in symbiosis with a hermit-crab, Eupagurus constans Stimpson, 

 and of forming " shells " of their own entirely composed of a chitinous 

 framework, so that in most specimens there is apparently no basis of 

 Gastropod shell, as is the case in most other known species of Hydractinia. 

 The skeleton of one of the species is totally devoid of spines, and its 

 substance is very thin and papery, while that of the other is rich, armed 

 with large spines, which are conical when small, but irregular in shape 

 and branching when large. 



Protozoa. 



Studies on Amcebae.§— A. Alexeieff describes two new species of 

 Amceba {A. densa and A. circumyranosa), and discusses encystation and 

 mitosis. There is no sign of any sexual process in connexion with the 

 encystation in A. punctata or A. Umax. In A. punctata the chromatoid 

 bodies are so large that it is difficult to believe that they are formed 

 from nuclear substances. In discussing the nuclear spindle the author 

 points out that the fibres cannot be regarded as directive threads for the 

 chromosomes. They vary greatly in their differentiation, and their 

 significance is simply that for physical and mechanical reasons the 

 plastin of the karyosome becomes more or less fibrillar when it is 

 dividing. 



Division in Amceba punctata. |1 — A. Alexeieff finds that the 

 equatorial plate is formed at the expense of the peripheral chromatin. 

 The formation of chromosomes is bound up with the presence of a 

 plastin substratum which is absent in the granules forming the equa- 

 torial plate. These should not, therefore, be called chromosomes. 

 There are no centrosomes, but their place is taken by polar bodies 

 which may be homologous. 



Division and Encystation of Amoeba limax 1[ — A. Alexeieff has 

 studied one of the Umax group of Amoebae, Amwba limax Duj. (emend. 

 Vahlkampf), which he obtains from hay infusions. The encystation 

 has not to do with any conjugation-process. In the mitosis the 



* Festschrift Richard Hertwig, i. (1910) pp. 305-22 (1 pi. and 2 figs.). 



t Arch. Zool. Exper., vi. (1911) pp. 325-52 (1 pi. and 16 figs.). 



X Journ. Exper. Zool., ix. (1910) pp. 469-96 (23 figs.). 



§ C.R. Soc. Biol , lxx. (1911) pp. 588-91 (40 figs.). 



|| Torn, cit., pp. 455-7. f Tom. cit., pp. 534-5. 



