4i8 



The I 



ournal o 



f Heredity 



about metamorphosis, although it does 

 produce growth in size. 



There is a most important difference 

 between the influence of the acti\e 

 implanted anterior lobe of the hypo- 

 physis on the one hand and on the 

 otlier the effects of feedini^ this inland. 

 In the case of im|)Iantation. metamor- 

 phosis is furthered through the co- 

 operation or intermediation of tlie thy- 

 roid glantl. This is e\idenced l)y the 

 effect of such implantation upon the 

 thyroid gland as explained abosc, and 

 by experiments performed b>' the 

 writer in which it was shown that 

 implantation of the anterior lobe of the 

 h\p<)plnsis of an adult frog into tad- 

 poles from which the tlnroid gland 

 has been removed does not produce 

 any tendency to metamorphosis even 

 though the implant is preserved in 

 normal condition. On the other hand 

 its implantation into normal tadpoles 

 hastens their metamorphosis and its 

 implantation into specimens from 

 which the hypoph^'sis has been re- 

 moved brings about their transforma- 

 tion, this being always accompanied 

 by increase in the size of the thyroid 

 gland. Keeping these facts in mind 

 and remembering that extirpation of 

 the antt'rior lobe of the hypophysis 

 pre\ents metamorphosis, allowing de- 

 \elopinent to proceed only to the point 

 attained in thyroidless tadpoles, we 

 ina>' conclude that there is an intimate 

 functional correlation between these 

 glands and that their co-operation is 

 essential to metamorphosis, unless ab- 

 normal amounts of iodine are adminis- 

 tered. 



A sharp distinction nuist be made 

 on the one hand between de\elopment 

 toward maturity regulated by the func- 

 tion. il co-operation of the thyroid 

 gland and the anterior lobe of the 

 hypophysis, and on the other hand the 

 ver\' distinct feature of size growth. 

 This size growth appears to be acceler- 

 ated by the action of the anterior lobe 

 of the hypo[)h\sis alone and is pro- 

 duced b\- substances-hormones stored 

 up in the gland and acti\e e\en in 

 dried pre|)arations. 



In this coiHiection it is most sig- 

 nificant that fe»-ding of dried tlnroid 



glands to tadpoles causes metamor- 

 phosis, not onh' in normal and thyroid- 

 less tadpoles, but also in tadpoles 

 deprived of the hypophysis and also in 

 tho.se deprived l)Oth of hypophysis and 

 thyroid gland. There is e\idence to 

 show that such thyroid feeding does not 

 operate so rapidh' toward bringing 

 about a shrinkage of the tail in tadpoles 

 deprived of the hypophysis as it does in 

 those that retain it in a functional 

 condition; but this demands more ac- 

 curate anaK'sis. 



It was pointed out abo\e that 

 Swingle accelerated metamorphosis in 

 normal tadpoles by feeding iodine and 

 that he produced it even in tadiKjIes 

 deprived of the thyroid gland. Allen 

 showed that iodine feeding would pro- 

 duce metamorphosis in tadpoles from 

 which the hypophysis had been re- 

 mo\ed and also in those from which 

 both hypophysis and tlnroid gland 

 had been remo\ed. 



We may from these facts conclude 

 that the process of metamorphosis 

 (growing mature) or these anuran 

 larvae can only take place under nor- 

 mal conditions in nature by the co- 

 operation of the thyroid gland and the 

 anterior lobe of the hypoplnsis, and 

 that the hormone thus formed is stored 

 in the thyroid gland. It is certain that 

 the most active chemical element in 

 tiiis iiormone is iodine and it is probable 

 that the colloid secretion that contains 

 this hormone is in the main active in 

 proportion to the amount of iodine 

 that it contains. We can not say 

 more at jiresent. The functioning of 

 these glands enables \ertebrates to 

 segregate the minute traces of iodine 

 that occur in their food and water and 

 to utilize it in furthering de\elopment 

 (metamorphosis in the amphibians). 

 In the absence of either or both of 

 these glands it is necessary to admin- 

 ister relatively enormous quantities of 

 iodine in order to accomjilish the results 

 normally attained through their agencN' 

 with the scarcel>' demonstrable traces 

 of iodine as it occurs in nature. 



.\ H.ASIS FOR I\Ti:KI'Ki:iIN<i IIIMAX 

 I'ROHI.ICMS 



These experiments ui)on amphibi.m 



