HORMONE FACTORS IN" GROWTH AND DEVELOPMENT 195 



glands. Allen (;) found that hypophysectomized tadpoles, though they 

 could not metamorphose if fed on normal food, would metamorphose upon 

 administration of thyroid gland or even iodin, and Hoskins and Hoskins 

 (c) recently demonstrated that thyroidectomized tadpoles at least begin to 

 metamorphose upon administration of anterior lobe. Larson found that 

 anterior lobe feeding in rats abolishes the effects of thyroidectomy. In 

 his last publication Allen (/) suggests that at least in amphibians the pitui- 

 tary gland may be necessary for the utilization of the iodin of the thyroid, 

 and calls attention to the similarity of the functions of both glands in 

 the amphibian organism. And indeed the role of the hypophysis in growth 

 and development seems to have much in common with the action of the 

 thyroid ; in particular the lowering of the carbohydrate tolerance, and, in 

 the absence of these glands, the lowering of the body temperature, the 

 retardation of growth and the atrophy of the sex glands are effects 

 common to both of them. 



Relation of (he Sex Glands to Growth and 

 Development 



One of the most important effects of the sex glands on growth and 

 development is shown in the development of the secondary sex characters. 

 The effects of castration have proved conclusively that these characters, at 

 least in many animals, are dependent upon the presence of the gonads. 

 The removal of the latter at an early (prepuberal) stage results in failure 

 to develop the secondary sex characters. The fundamental changes fol- 

 lowing castration in man (Tandler and Grosz (a) (b) (c) (<#)), in cattle 

 (Sellheim (b) (c), Tandler and Keller), in deer (Rb'hrig), in guinea pigs 

 and rats (Halban, Steinach, Marshall and Jolly, Hatai) afford sufficient 

 proof of an intimate relationship between the sex glands and secondary sex 

 characters. The removal of the sex glands before puberty causes the exter- 

 nal genitalia to remain infantile and inhibits the development of the acces- 

 sory reproductive organs, and of many external characters differentiating 

 the male and female of the species. Similar relations exist among birds 

 (Goodale, Morgan, Pezard), amphibians (Nussbaum, Harms, Bresca) and 

 even among organisms as low as the crustaceans (Girard, Smith). 



The sex glands control development, not by nervous connections, but 

 by the elaboration of a specific internal secretion. If the mammary gland 

 of a young rabbit is removed from its place and grafted to the ear of the 

 same animal, it will develop like a normal gland, although its nervous con- 

 nections have been severed. It may even form the structures of a secretive 

 mammary gland and produce milk when the host becomes pregnant (Rib- 

 bert). Moreover, the regrafting of sex glands into castrated animals shows 



