426 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Biogeographical Regions.* — A. Jacobi has made an important 

 contribution to biogeograpby. He accepts the -fundamental idea that 

 tbe present distribution does not correspoDd, in many cases, to the 

 present conditions of life, but bas often its origin in the past, and 

 indicates conditions prevailing in former geological periods. 



He finds in Lydekker's Arctogaea, Neogsea, and Notogasa, the most 

 appropriate division applicable to tbe distribution of mammals and birds 

 since the beginning of Tertiary times. 



But there are numerous facts which show in certain parts of the 

 earth a faunal and floral distribution which is inexplicable by the 

 present conditions. Thus Jacobi distinguishes fifteen " areas of dis- 

 persal " (Ausbreilungsgebiete), which demand a former land-connection 

 between areas now more or less separated. 



" In the demonstration that such conditions must have existed in 

 former times, and in the collection of known facts as well as in the intro- 

 duction of new ones, which tend to support this assumption, lies tbe 

 chief value of Jacobi's paper, which will be of great use to any one who 

 proposes to study these highly interesting zoogeographical questions." 



Plankton of the Lake of Maria-Laach.t— 0. Zacharias reports on 

 the Algae, Flagellata, Rotatoria, Crustacea, and Hydrachnida of this lake 

 in the Coblenz district. The most interesting fact is, that some Crustacea, 

 e.g. Dioptomus cseruleus and Hydrachnids, e.g. Atax crassipes, showed 

 degeneracy as regards size — which may be reasonably correlated with 

 tbe continual ascent of bubbles of carbonic acid gas from the floor. No 

 effect on Rotifers was noticed, but Diatoma tenue was more slender and 

 delicate than in any other water-basin investigated. 



Tunicata. 

 New Giant Pyrosoma-I — J' Bonnier and C. Perez observed in the 

 Indian Ocean an immense shoal of gigantic specimens of Pyrosoma 

 indicum sp. n., all swimming in the same direction but at different 

 depths. The smallest, 40-50 cm. in length, were almost on the surface ; 

 the largest, 2*50 m.in length, with a diameter of 20-30 cm., were swim- 

 ming about 2 m. from the surface. The ascidiozoids were bright red, 

 with remarkable development of a powerful spindle-shaped lateral 

 muscular band (200 /i broad by 1500 p. long). The gut contained a 

 monocystic Gregarine, doubtless allied to Lankesteria ; the cavity of 

 the colony included commensal iishes and a Peuasid. 



INVERTEBBATA. 



Mollusca. 

 ■y. Gasteropoda. 



New Parasitic Gasteropod in Holothurian.§ — Kristine Bonnevie 

 describes a very interesting new form — Enteroxenos ostergreni g. et sp. n. 



found by Hjalmar Ostergren in 1896, as a parasite in Stichopus 



tremulus. 



* Zeitschr. Ges. Erdkunde Berlin, xxxv. (1900) pp. 147-238 (2 pis.). Review by 

 A. E. Ortmann, Amer. Nat., xxxvi. (1902) pp. 157-9. 

 t Zool. Anzeig., xxv. (1902) pp. 395-6. 

 X Comptes Rendus, cxxxiv. (1902) pp. 1238-40. 

 § Zool. Jahrb., xv. (1902) pp. 731-92 (5 pis. and 6 figs.). 



