332 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



Spina bifida in very early Human Embryo. — S. T. Wallis Cull 

 {Bull. Johns IIopJci7is Hospital, 1910, 30, 181-3, 1 fig.). An embryo 

 17 mm. long, perhaps seven weeks old, showed abnormalities of brain, 

 spinal cord, viscera and skeleton generally supposed to be characteristic 

 only of much older monsters. The chief point of pathological attack 

 seems to have been in the axial skeleton and central nervous system 

 below the brain. The popular conception that mechanical influences 

 have an important bearing upon the formation of monsters has been 

 overthrown by recent chemical experiments. The specific action of 

 dilute salt solutions upon Amphibian eggs, for instance, will produce 

 spina bifida in a large proportion of the embryo. The trouble would 

 seem to lie, therefore, not in the ovum itself, nor in the external 

 mechanical infiuences acting upon it at a later date, such as amniotic 

 bands which compress the umbilical cord, but rather in the impairment 

 of nutrition associated with faulty implantation, or in the toxic influences 

 arising from a diseased uterus. J. A. T. 



Influence of Thyroid on Growth and Development of Amphibia. 

 — E. R. and M. M. Hoskins (Journ. Exper. Zool, 1919, 29, 1-70, 

 9 pis.). Experiments on Anihly stoma punctatum and Rana sylvatica, 

 from which the thyroid was removed at an early stage before it had 

 begun to differentiate. The thyroidless larvae grow much larger than 

 the controls. They do not exhibit metamorphosis within a year. 

 Probably they cannot undergo it at all. This is attributed to faulty 

 metabolism, e.g. of calcium. There is deficiency in calcification and 

 ossification. Thyroidless forms show (1) slow growth, slow differentia- 

 tion, and large size of brain ; (2) a relatively large liver imperfectly 

 differentiated ; (3) hyperplasia of the hypophysis ; (4) eventually large 

 thymus and epithelioid (parathyroid) bodies ; (5) relatively large 

 kidneys ; (6) a long intestine of a larval character ; (7) large ovaries 

 without mature ova or oviducts ; (8) prematurely mature testes, pro- 

 ducing spermatozoa. The internal gills persist in animals kept in the 

 larval condition by thyroidectomy. The lungs develop and become 

 functional in both normal and thyroidless larvae. J. A. T. 



Inbreeding-effects in Albino Rats. — Helen Dean King {Journ. 

 Exper. Zool., 1919, 29, 71-111, 8 charts). The closest form of in- 

 breeding possible in mammals, the mating of brother and sister from 

 the same litter, is not' necessarily inimical either to body growth, to 

 fertility, or to constitutional vigour, provided that only the best animals 

 from a relatively large number are used for breeding purposes. Selec- 

 tion, seemingly, is able to hold in check any tendency that inbreeding 

 may have to brijig out the undesirable latent traits inherent in the 

 strain. Adverse conditions of environment and of nutrition produce 

 far more detrimental effects on growth and fertility than does inbreed- 

 ing. But these factors do not alter to genetic constitution. The sex 

 ratio seems amenable to selection, for two lines were separated out. 

 The effects of selection were not cumulative however. It is quite clear 

 that long-continued inbreeding did not change the normal body-weight 

 relations of the sexes, nor the form of the growth graph to any note- 

 worthy extent, nor rate and extent of growth in weight. J. A. T. 



