208 GENERAL ZOOLOGY 



be evoked out of season by implanting anterior lobe tissue. 

 Ovulation may be produced by anterior lobe tissue from either 

 male or female frogs. 



Thyrotropic Hormone. — There is a close functional relationship 

 also between the anterior pituitary lobe and the thyroid gland. 

 If the anterior lobe of the frog tadpole is removed, metamorphosis 

 fails to occur. The thyroid gland of such animals is highly 

 atrophic, a condition that can be corrected by transplanting 

 anterior pituitary tissue or injecting pituitary extract. In either 

 case the thyroid gland is restored to normal condition and 

 metamorphosis follows. Metamorphosis seems to require the 

 presence of a normal thyroid gland in the tadpole. Thus removal 

 of the thyroid gland in tadpoles prevents metamorphosis; feeding 

 thyroid or thyroid extract to such tadpoles results in a completion 

 of metamorphosis; and feeding thyroid gland to normal tadpoles 

 hastens metamorphosis. The thyroid hormone is the immediate 

 cause of metamorphosis, but the thyrotropic hormone of the 

 anterior pituitary is necessary for its normal functioning. 



Lactogenic Hormone. — An extract has been obtained from the 

 anterior pituitary gland, which when injected into female 

 rabbits, dogs, or pigs, causes a secretion of milk in the mammary 

 glands, without increasing the amount of the mammary tissue. 

 It is interesting that such extracts obtained from beef or sheep 

 pituitary glands also stimulate the formation of "pigeon milk" 

 in the crop glands of male or female pigeons. The crop glands 

 of pigeons normally produce pigeon milk only when young are 

 being reared. 



Adrenotropic Hormone. — One of the effects of removing the 

 anterior pituitary from rats is a degenerative change in the 

 cortex (outer layer) of the adrenal glands, which can be restored 

 by the implantation of pituitary tissue. An extract of the 

 anterior pituitary lobe has been made that is high in adrenotropic 

 activity. The relation of the adrenotropic hormone to the 

 adrenal gland seems to be similar to the relation of the thyrotropic 

 hormone to the thyroid. That is to say, both glands depend upon 

 hormones from the anterior pituitary lobe for the performance 

 of their normal functions. 



In addition to these five well-known anterior pituitary hormones 

 there is also evidence of endocrine relationship between the 

 anterior pituitary lobe and the islet cells of the pancreas or 



