ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 297 



-and finds that the thymus diet accelerates development up to the stage 

 when worm-fed larvae go into metamorphosis. At that point develop- 

 ment of most organs seems to stop, and disturbances often fatal ensue. 

 There is apparently the .suppression of some factor, without which further 

 •development is impossible. Severe tetany occurs. The acceleration of 

 -early growth and development seems to be the effect of quantitative 

 conditions, and not the result of a specific quality of the thymus, such 

 as a specific growth-stimulating agent. The thymus gland apparently 

 contains all the nutriment necessary to build up an amphibian organism, 

 for specimens of Amhlystoma punctatum, kept at low temperature, were 

 reared on thymus diet from the fourteenth day to the fourteenth month. 



J. A. T. 



Effects of Underfeeding Young Albino Rats.— Chester A. 

 Stewart {Journ. Exper. ZooL, 1918, 25, 301-353, 1 fig.) removed 

 newborn rats from the mother for nearly one-half of the total time for 

 the usual three weeks of nursing. Great retardation of growth resulted. 

 There is a progressive tendency in the skeleton and (to a slight extent) 

 in the musculature to increase in weight, counterbalanced by a decrease 

 in the integument and viscera. There is great diversity as regards the 

 individual organs, and in regard to this detailed measurements are 

 submitted. J- ^- T. 



Grafts in Amblystoma. — E. Uhlenhuth (Journ. Exper. ZooL, 

 1017, 24, 237-301, 5 pis., 3 figs.), working with larvae of A. pimc- 

 tatim, grafted the two halves of the skin of the head, including an eye, 

 on to two other larvae. The skin grafts developed the network and the 

 yellow spots, not simultaneously with each other, but simultaneously 

 with their hosts. They metamorphosed only if the host did. Skin 

 from A. punctatum, grafted on to A. tigrinum, metamorphosed there, 

 and in the same time-relation as on a host of the same species. It seems 

 that the development of the yellow spots of A. punctatum depends on 

 two factors. One factor is responsible for the kind of yellow spots that 

 will develop, and is contained in the skin itself. The other factor, 

 which may be called the " metamorphosis factor," is necessary to start 

 the developrueut of the yellow spots, i.e. the metamorphosis of the skin; 

 it is not contained in the skin ; it is produced by the body or some 

 particular organ ; it is non-specific ; it may be identified with an agent 

 like thyroid-substance. J- A. T. 



Sexual Activity of Male Rabbit in Relation to Progeny. — Frank 

 A. Hays {Journ. Exper. Zool., 1918, 25, 571-613, 22 charts) finds 

 no inferiority in body-weights of offspring from heavy service groups, 

 nor in body growth, nor in vigour. Heavy service of males gives a 

 perceptible decrease in the proportion of male to female offspring. 

 Female offspring are, to some degree, more likely to succumb than male 

 offspring in all service groups, except the twentieth. The high per- 

 centage of deaths of female progeny is largely due to the predominance 

 of females to males in the litters. " By no means thus far used has 

 any inferiority of progeny from heavy sexual service been discovered. 



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