INSECT METAMORPHOSIS. 



mori L. fed on mulberry leaves sprayed with thyroid extract is 

 normal and that the "thyroid" animals are smaller than the 

 controls. The accelerating influence of the thyroid food was 

 however noticed in the second generation of the insects under 

 examination. We see that the results of my "thyroid" experi- 

 ments are in complete agreement with those performed by Terao 

 and Wakamori on the first generation of the animals. Unfortu- 

 nately I have been unable to examine the second generation 

 of my moths. 



I will not discuss here the relation of the lack of any influence 

 of thyroid on the rate of metamorphosis of the insects experi- 

 mented upon to the problem of the physiology of metamorphosis 

 in these animals. As I have emphasized elsewhere (Kopec, '23), 

 only positive results of the experiments on the influence of 

 glands of internal secretion may be considered as decisive in this 

 respect and only to a certain degree. It is not impossible that 

 the negative influence exerted in my experiments on the weight 

 of caterpillars by thyroid feeding is not due to specific checking 

 of growth faculties, but rather to certain changes elicited in 

 their digestion by a totally foreign substance. Such caution is 

 the more advisable, as we have already certain data in the 

 literature, which point to positive effect exerted on " lower >! 

 animals by substances of glands of internal secretion from 

 vertebrates. Nowikoff ('08) remarks an increase of the rate of 

 multiplication of infusorians reared in aqueous extracts of the 

 thyroid gland. Hanko ('12) observes a positive influence of 

 extracts of hypophysis on the rate of moult, regeneration and 

 growth in Asellus aquations. The thyroid gland has, according 

 to Wulzen ('16) a positive influence on the rate of division and 

 growth of Planaria maculata. From the experiments of van 

 Herwerden ('23) we see that the cortical substance of adrenals 

 of the ox has an accelerating influence on the multiplication of 

 Daphnia pulex as well as on growth of this crustacean and of 

 young specimens of Limncea stagnalis. I believe however that 

 only a larger experimental material may constitute a base for 

 general discussion on the influence of glands of internal secretion 

 of vertebrates on processes taking place in invertebrates. 



The opinions of separate authors as to the relation of growth 



