296 SUMMARY OF CURRENT RESEARCHES RELATING TO 



number of g;erm-cel]s, interstitial cells and other tissue elements in the 

 gonads. Starvation greatly ret<irds the normal cycle of development of 

 the germ-cells, and prevents the onset of sexual differentiation. 



J. A. T. 



Thyroid-feeding of Tadpoles. — W. W. Swingle {Joum. Exper. 

 Zool, 1918, 24, 521-43, 11 tigs.) finds that by feeding thyroid extract 

 to frog larvEe great bodily changes are brought about within a very few 

 ■days ; entire organs and systems are transformed with startling rapidity 

 from the larval condition to that characteristic of the adult. Yet in the 

 midst of such somatic transformations the gonads and germ-cells remain 

 unaffected. In a state of nature it requires two seasons, and sometimes 

 three, for the larvEeof Rana cateshiana to reach the adult condition. It 

 is possible by judicious thyroid feeding to bring about almost complete 

 metamorphosis within a period of three weeks in the immature larva3 of 

 this species of frog. The animals have all the body characteristics of 

 the metamorphosed frog, yet the germ-cells and germ-glands are those 

 of young larvse. J- A. T. 



Removal of Thyroid from Tadpoles.— Bennet M. Allen iJourn. 

 Exper. ZooL, 1918, 24, 499-519, 1 pi., 8 figs.) finds that absence of the 

 thvroid gland in the tadpoles of Rana pipiens does not affect the course 

 of'early development up to the time when the hind limlis have begun to 

 grow. Further differentiation of the soma — form of body, limbs, gut, brain, 

 ^tc. — ceases, and metamorphosis does not occur. Thyroid administration 

 to thyroidless tadpoles brought about a resumption of development even 

 four months after it had ceased. The removal of the thyroid does not 

 affect gonads and germ-cells. J. A. T. 



to*- 



Effect on Ossification in Tadpoles of Extirpating Thyroid.— George 



S. Terry (Journ. Exper. Zool, 1018, 24, 5G7-87, 2 pis., 2 figs.) experi- 

 mented with tadpoles of Rana pipiens and found that the vertebra; of 

 thyroidless tadpoles continue to grow long after the normal time ; that 

 they retain primitive characters, e.g. in having little in the way of 

 spinous process ; and that they show almost no trace of ossification. The 

 removal of the thyroid greatly retarded, if it did not completely stop, 

 both ossification and growth in the bones of the hind leg. Calcification 

 of the cartilage is proceeded with, but there is extreme retardation in 

 the process of ossification. J- A. T. 



Effect of Thyroid Extirpation on Thymus and Pituitary Glands. 

 —James B. Rogers (Journ. Exper. Zool, 1918, 24, 589-605, 1 pi., 

 2 charts) has experimented with tadpoles of Ra7ia jnpietis, and finds 

 that the pituitary and thymus glands continue to develop when the 

 thyroid gland is extirpated. The pituitary gland may be larger than in 

 the controls. The young sexually mature frogs have smaller thymus 

 glands than thyroidless tadpoles of the same age. The thymus glands 

 of thyroidless tadpoles do not migrate to the position occupied in adult 

 frogs, and do not degenerate like those of normal frogs. J. A. T. 



Influence of Thymus-feeding. — Eduard Vklenrvth (Journ. Exper. 

 Zool, 1918, 25, 135-55) has experimented with larva of Amhly^toma, 



