40 E. R. HOSKINS AND M. M. HOSKINS 



of the growth does have some influence on the rate of develop- 

 ment of the ovary, but the effect is not different from the effect 

 upon various other organs and is not characteristic of the gonads. 



Allen ('18, pp. 513, 514) emphasises the fact that in estimated 

 volumes the ovaries of old thyroidless larvae are about four 

 times as great as those of young frogs, but he does not note that 

 such larvae themselves are from three to six times the size of 

 such frogs. Hence in relative size the frogs have the larger 

 ovaries. The growth of the ovaries in absolute size in these 

 thyroidless larvae resembles the growth of other organs, such 

 as the liver, thymus, heart, etc. 



Other evidence of the fact that rapidity of growth plays a 

 part in the development of organs of animals in similar stages 

 of development is shown by the ovaries of the newly metamor- 

 phosed frogs of the 1917 and 1918 series. In the former, which 

 as stated above grew more slowly and did not metamorphose 

 until August, the ovaries are slightly further advanced in de- 

 velopment than in the latter, which grew more rapidly and 

 metamorphosed in June. In the former the oocytes are evident 

 on the surface of the ovary and the ovary has an adult shape, 

 whereas in the latter the ovary is often still flat and oocytes 

 are but very faintly indicated on the surface. It is also true, 

 however, that organs other than the gonads were further ad- 

 vanced in these 1917 frogs than in the younger 1918 frogs. 

 Further, as stated above, if the control larvae could in some 

 way be induced to grow as large as these thyroidless larvae 

 their ovaries would doubtless also become larger before meta- 

 morphosis. 



An increase in size is a matter of growth rather than of differ- 

 entiation. The latter process may be said to be complete in 

 the ovary when maturation occurs, as the eggs leave the ovary. 

 Maturation has not been seen in the ovaries of our thyroidless 

 larvae, even when they have been kept alive through the second 

 season, and therefore the experiments do not prove that the 

 ovaries are independent of the soma in their development. We 

 cannot agree with Allen's statement that thyroidectomy demon- 

 strates a sharp difference between the gonads and tlie remainder 



