284 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



an excess of 84 p.c, the testes of 12 p.c. The hypophysis and siipra- 

 renals respond differently to exercise in the two sexes. They show, as 

 the result of exercise, an approach to the relations characteristic for the 

 Norway rat. The exercised rats, were either entirely free from lung- 

 infection or but slightly affected. The control rats were badly infected. 

 Lung infection is not responsible for the changes observed in the organs. 

 Exercise for 30 days showed in most organs modifications similar to 

 those observed in rats exercised for 90-180 days. In the exercised rats 

 the heart-weight and amount of exercise taken are highly correlated. 



Growth and Weight in Albino Rat.* — Helen Dean King finds 

 that in similar environmental conditions the growth of rats within a 

 given colony tends to be uniform ; but in dissimilar conditions different 

 weights result for the same ages. The male is usually heavier than the 

 female at birth and afterwards, but the female increases in weight much 

 more rapidly than the male during the early stages of development and 

 reaches her maximum much earlier. Variability in the body-weight, as 

 measured by the co-efficients of variation, is greatest when the animals 

 are about GO days of age. It decreases slightly at 90 days, and after 

 120 days remains practically constant until the animals are about one 

 year old. Very young female rats seem to show as great a range of 

 variability in body-weight as do the males, but the males are more 

 variable than the females at all later stages of growth. The average 

 co-efficient of variation for the body-weights of the 50 male rats used 

 in the investigation was 1?)"6; that for the females 12 "l. There is 

 apparently a direct correlation between the rapidity of growth and the 

 variability in body-weight after the animals have reached 60 days of 

 age. Fraternal variability is less than racial variability ; for the male 

 about 70 p.c. of that of the general population, for the female about 

 55 p.c. 



Development of Lymphatic System.j — Charles F. AY. McClure 

 asks whether the endothelium of the lymphatic system arises, at any 

 place or time, in a discontinuous manner and independently of that of 

 the veins. His answer is that the development of the general vascular 

 system — both hfemal and lymphatic vessels — is a uniform process, 

 which consists in a local genesis of endothelium from mesenchymal cells 

 and a growth of endothelium after it has once been formed. The 

 lymphatic problem, in its broadest sense, should not be interpreted in 

 terms either of a venous or non-venous origin, but rather in terms of 

 the uniform phases of genesis and growth which may characterize the 

 establishment of vascular channels in general. 



Mesenchyme Cells of Teleost Yolk-sac.+ — Charles E. Stockard 

 has studied the wandering mesenchymal cells on the living yolk-sac, 

 and their developmental products — chromatophores, vascular endo- 

 thelium and blood-cells. The yolk-sac has only one really definite 



* ADat. Record, ix. (1915) pp. 751-76 (5 figs.) 



t Anat. Record, ix. (1915) pp. 563-79. 



X Amer. Journ. Auat., xviii. (1915) pp. 525-94 (35 figs.). 



