592 JAMES B. ROGERS 



MIGRATION OF THE THYMUS GLANDS 



Results 



In the course of this work it was found that the thymus 

 glands of normal animals migrate in the process of metamor- 

 phosis. In normal tadpoles the thymus gland is found ventral 

 and posterior to the eye and attached to the skull by connec- 

 tive tissue. In the metamorphosing frog as the head is taking 

 on adult characters the thymus gland is found to have migrated 

 posteriorly to a point just ventral to the tympanum. In the 

 adult frog it is found in a mass of connective tissue under the 

 depressor mandibuli muscle, thus coming to lie ventral and 

 posterior to the tympanum. The thyroidless tadpoles still 

 have the glands close to the eye and anterior to the tympanic 

 membrane. 



When the frog reaches the stage of sexual maturity, the 

 thymus is flattened. This is due to its position between the 

 muscles. In going from the tadpole to the recently meta- 

 morphosed frog stage it will be noticed in the drawings that there 

 is sudden decrease in the size of the thymus glands and at the 

 same time the glands become more globular. This is attributed 

 to the loss of water from the tissues at metamorphosis. Ref- 

 erence to tables 1 and 2 will show that there is a decided shrink- 

 age of the body at the time of metamorphosis, which is to be 

 seen at a glance by any one who has reared them. It is not 

 surprising that there should be shrinkage of the pituitary and 

 thymus glands. 



The pituitary and the thymus glands vary much in size and 

 these differences can not always be explained by a correspond- 

 ing difference in body length. This is strikingly shown by 

 examination of the class of normal tadpoles, specimens 5 to 10, 

 which were killed in July (table 2). Control 5 has a body 

 length of 27 mm. and a pituitary gland represented by 58 as 

 determined by the method explained above. Control 10 has 

 a body length of 34 mm. and a pituitary gland represented by 

 224. This shows a development of the pituitary gland corre- 

 sponding with the development of the tadpole. 



