216 



SCIENCE 



[N. S. Vol. XLVI. No. 1183 



incorrect. In addition to mathematical 

 problems and random notes on elementary 

 mathematics through the calculus there are 

 similar notes on astronomy and the calendar, 

 and on mechanics and physics. 



Louis C. Kaepinski 



SPECIAL ARTICLES 



THE EFFECTS OF THYROID REMOVAL UPON 



THE DEVELOPMENT OF THE GONADS IN 



THE LARV^ OF RANA PIPIENS 



In a paper published in Science, November 

 24, 1916, a general account was given of my 

 experiments performed in the spring of 1916 

 upon the removal of the anlagen of the anterior 

 lobe of the hypophysis and of the thyroid gland 

 in early tadpoles of Bana pipiens. It was 

 shown that in each case this operation pre- 

 vented metamorphosis. A full account of the 

 results of the removal of the anterior lobe of 

 the hypophysis has been published.' 



ISTow the effect of thyroid removal upon the 

 development of the gonads has been largely 

 worked out. A full account of this latter phase 

 of the work will be published in due time, to- 

 gether with papers by students of mine who 

 have worked along correlated lines. It seems 

 desirable in the meantime to give a brief ac- 

 count of the most interesting theoretical re- 

 sults of my investigations. 



It was shown in my earlier paper that in the 

 absence of the thyroid gland the tadpoles 

 failed to undergo metamorphosis. Development 

 went on normally up to the time when the 

 hind limbs reached a length of 4^5 mm. At 

 this stage the limbs entirely ceased to develop 

 while the body as a whole failed to undergo 

 further differentiation. Wliile the tadpoles 

 increased very greatly in size they at no time 

 showed any further evidences of metamor- 

 phosis. This was true in spite of the fact that 

 they eventually attained a length of body- 

 exclusive of tail — varying from 30 to 43 mm. 

 These figures are far in excess of any length 

 normally attained by tadpoles of this species. 

 From time to time specimens were killed and 

 studied. At the date of writing, March 20, 

 two of these tadpoles still remain alive and are 



1 Biological Bulletin, March, 1917. 



in the same stage of bodily differentiation that 

 they had reached the last of June. 



This not only involves leg length, the failure 

 of the tail to decrease in length and the failure 

 of the mouth to change in form, but it involves 

 the retention by the intestine of the original 

 relative length characteristic of tadpoles. The 

 lateral line organs became more highly devel- 

 oped than ever. In short a strictly larval form 

 is maintained for months. 



Now it is true that failure to metamorphose 

 may likewise be attained by insufficient feed- 

 ing if brought about at a sufficiently early 

 stage of development. One larval tadpole with 

 hind legs 5.5 mm. in length was kept in its lar- 

 val condition by feeding very meagerly to No- 

 vember 15. At that time an effort was made 

 to cause it to increase in size and to attain 

 metamorphosis. Although it ate food it re- 

 mained quite small, not showing any marked 

 increase in size, nor did it show any strong 

 tendency toward metamorphosis. When killed 

 Febaruary 22 the testes were fomid to be quite 

 small, they showed spermatogonia but no 

 tendencies toward spermatogenesis. This 

 was in strong contrast to the condition in a 

 thyroidless tadpole with a body length of 43 

 mm. killed February 7. In this tadpole the 

 testes were well developed, spermatogenesis 

 was most active and thousands of completely 

 formed spermatozoa were found in the testes, 

 although the tadpole had remained in a strictly 

 larval form with hind limbs only 5.5 mm. long 

 and with a stomach and intestine length of 

 426 mm. — over 12 times the length of the cor- 

 responding organs in normal frogs at the time 

 of metamorphosis. 



The above cases are compared in order to 

 show that although starvation may serve as 

 one means of retarding metamorphosis, it also 

 retards the development of the gonads and of 

 the contained germ cells. This has been thor- 

 oughly established in an unpublished paper 

 by Mr. Wilbur Swingle, one of my graduate 

 students who carried out a series of experi- 

 ments upon this same species. This case is 

 cited to obviate the objection that the condi- 

 tions here set forth might have been produced 

 by starvation and not in thyroidless tadpoles 



