194 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Growth-period and Duration of Life.* — John N. Northop has 

 experimented with larvae of Drosophila, whose growth can be greatly 

 retarded by growing them on sterile fruit or other substances containing 

 no yeast. The deficiency is probably in " vitamines," or growth- 

 promoting substances. The prolongation of the larval period is without 

 effect on the duration of the pupal period, but the total duration of life 

 can be prolonged. This shows that the relative durations of the larva, 

 pupa, and imago stages are independent. It is probable that the duration 

 of each of the stages is determined by the formation (or by the 

 disappearance) of a definite specific substance. 



Study of Structure, Habits, and Life-history of Hylastes. f — 

 James W. Munro has made a valuable study of this genus of Scolytid 

 bettles, three-species of which are of considerable interest to the forester, 

 namely Hylaster ater, H. palUatus, and H. ctmicularius. All the three 

 attack Conifers. A well-illustrated account is given of the external 

 features, the appendages, the alimentary canal, and the reproductive 

 organs. The mother-galleries and the larval-galleries in the roots of the 

 Conifers are described. The life-histiories of the three are carefully 

 contrasted, and the economic importance of the insects is discussed. The 

 illustrations of this very useful paper are of great merit. 



Endoskeleton of Head and the Coxal Cavities of Beetles.:}: — 

 Thomas G. Sloane has studied the endoskeletal plate and its supports 

 inside the head of Carabidae and Cicindelidae. They serve for the 

 support of the muscles of the mouth-parts. Their differences in the 

 two families are indicated. He also deals with the structure of the 

 anterior coxfe, and with the different forms of anterior coxal cavities in 

 the Carabidae. The facts do not seem to the author to support the 

 current view that the open anterior coxal cavities are more primitive 

 than the closed cavities. 



Germ-cell Cycle of Dineutes nigrior.§— R. W. Hegner and C. P. 

 Russell find that in this whirligig beetle an ultimate oogonium divides 

 into two daughter-cells of unequal size. The smaller gives rise to 

 nurse-cells only. The larger, " the oocyte grandmother-cell," contains 

 an oocyte determinant. Its division into four cells is differential, for 

 one product, " the oocyte mother-cell," receives all of the oocyte deter- 

 minant, the other three lack this body and become nurse-cells. Each 

 of these four cells undergoes a single mitotic division resulting in the 

 formation of seven nurse-cells and one oocyte, the latter containing the 

 oocyte determinant. In Dytiscus there are four differential divisions,, 

 and the oocyte is accompanied by fifteen nurse-cells ; in Dineutes nigrior 

 there are three differential divisions, and the oocyte is accompanied by 

 •seven nurse-cells. 



* Journ. Biol. Chemistry, xxxii. (1917) pp. 123-6. 



t Proc. Roy. Phys. Soc. Edinburgh, xx. (1917) pp. 123-58 (28 figs.). 



I Proc. Linn. Soc. N.S.W., xlii. (1917) pp. 339-42. 



§ Proc. Nat. Acad. Sci. U.S.A., ii. (1916) pp. 356-6 (6 figs.). 



