546 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



not in itself sufficient. Nitrifying organisms do not appear regularly in 

 the sea ; they arise in the neighbourhood of the continental coasts, and 

 thus the operation of denitrifying bacteria is limited. 



Of great importance are the vertical convection-currents which bring 

 the sinking dead plankton to the surface again, and thus enrich the 

 nutritive supply at the surface and allow a stronger development of the 

 plankton. In the Mediterranean, with its very slow vertical circulation, 

 the plankton is sparse, but where there are vertical currents, as at 

 Messina and on the coast of Algiers, it is much richer. This view 

 explains local accumulations of plankton as well as the general distribu- 

 tion. In high latitudes the vertical currents are more marked than in 

 temperate seas ; the plankton maximum is at the equator. Many 

 particular cases as well as the general facts show that wherever there are 

 well-developed vertical currents there the plankton is quantitatively rich. 



Migration of Plankton in Lakes.* — E. Monti points out that in 

 small shallow clear lakes of the high Alps there is a horizontal migration 

 of the Crustaceans which is apt to vitiate the method of samples. The 

 Entomostraca leave the parts of the surface which are sunny or moved 

 by the wind, and seek the shaded parts. This migration often leads to 

 an accumulation of the whole mass of the plankton in a single bay, and 

 it also affects the vertical distribution. 



Arctic Biological Station.f — Martin E. Henriksen reports that a 

 biological station is about to be established on Disco Island, off Green- 

 land, " a well-chosen vantage-ground for the study of arctic biology." 

 It will be open free to investigators, who should communicate with the 

 director, M. P. Porseld, University, Copenhagen. The money for the 

 erection of the station has been supplied by P. Hoick, of Copenhagen, 

 and the Danish Government will pay the current expenses. Everyone 

 will wish this new station all success. 



Momentum in Variation.! — F. B. Loomis gives a number of 

 examples — e.g. the crania and teeth in sabre-toothed tigers, horns of 

 Cervidas, septal edge in Ammonites — to show " that as a special feature 

 develops, it attains a momentum which tends to carry it beyond the 

 point of greatest utility." "A variation started along any line tends 

 to carry that line of development to its ultimate, being driven by 

 momentum." " This factor of momentum has not been given the 

 importance due to it, . . . it should find an important place in the 

 explanation of animal structures." But unless the author can translate 

 momentum into biological terms, he has merely suggested a metaphor. 



Marine Fossils from Crete.§ — R. A. Bullen records from a large 

 Mammalian bone, of Pleistocene age, found in a cave at Kharoumes, 

 East Crete, a number of Foraminifera, two Polyzoa, valves of Entomos- 

 traca, and several marine Mollusca. Their evidence, along with other 

 data, points to oscillations of the land surfaces, leading to their sub- 

 mergence and re-emergence. 



* Rend. R. 1st. Lombardo, xxxviii. (1905) pp. 122-32. 

 t Biol. Centralbl., xxvi. (1906) p. 256. 

 + Amer. Nat., xxxix. (1905) pp. 839-43 (2 figs.). 

 § Geol. Magazine, No. 506 (1906) pp. 354-8 (2 pis.). 



