448 SUMMARY OF CURRENT RESEARCHES RELATING TO 



small chambers on the side of a stolon, containing nutritive material 

 and blood-cells, covered with epithelium and tunicin. Inside these buds 

 a complete Ascidian is built up. 



INVERTEBRATA. 



Mollusca. 

 y. Gastropoda. 



Environmental Studies on the Limpet.* — E. S. Russell seeks to 

 correlate certain modifications of the shell of Patella vulgata with 

 definite environmental conditions. As to the homing habit, he con- 

 cludes that every limpet of 15 mm. and upwards, occupies for long 

 periods at a time a definitely fixed position to which it returns after 

 any wanderings that it may make for food ; that limpets under 

 15 mm., if not yet settled in a definite position, never wander far away, 

 and generally keep to the same stone. The movements are chiefly when 

 covered by the tide. High-water and low-water limpets differ in 

 definite ways, which are carefully tabulated. Adult exposed shells are 

 lower spired, narrower, thicker, and more irregular than sheltered shells. 

 An interesting conclusion is that the " rough " types occur on rough 

 stones ; the " smooth " types (var. cmrulea) on polished stones. A small 

 change in an environment may produce through its continuous action a 

 large cumulative result by a summation of successive little effects. 



Experimental Dwarfing of Water-snails.f — R. Legendre has 

 experimented with Lymnmns stagnalis and Planorbis corneus, rearing 

 parts of the same brood in varied conditions. He finds, as previous 

 experimenters have done, that it is not difficult to produce dwarf forms 

 by crowding. Unlike Semper and De Varigny, however, he finds reason 

 to believe that the excreta in the water act in an inhibitory manner on 

 growth. 



Philomycus.J — Y. Sterki makes some notes on this genus of nearctic 

 slugs, which is distinguished from Limax by having the mantle extended 

 over almost the whole body. He defines a few species, and proposes to 

 give the genus the attention which it merits. 



8. Iiamellibranchiata. 



Parthenogenetic Development in Mactra.§ — K. Kostanecki found, 

 in 1905, that a potassium chloride sea-water solution served as a stimulus 

 to the parthenogenetic development of the eggs of Mactra. In studying 

 the matter further, he finds that there is mitotic nuclear division without 

 corresponding cell-division. 



Structure of Phaseolicama magellanica.|| — J. Igel gives an ana- 

 tomical description of this bivalve, which occurs under stones on the 



* Proc. Zool. Soc, 1907, pp. 856-70 (12 figs.). 



f Arch. Zool. Exper., viii. (1908) Notes et Bevue, No. 3, pp. lxxvii.-lxxxiv . 



% Ohio Naturalist, viii. (1908) pp. 265-6. 



§ Bull. Internat. Acad. Sci. Cracovie, 1908, pp. 97-101 (1 fig.). 



|| Zool. Jahrb., xxvi. (1908) pp. 1-44 (2 pis.). 



