350 STEFAN KOPEC. 



to metamorphosis are not as yet in agreement. While for 

 certain authors metamorphosis is a function of growth for 

 others there is no essential connection between the two processes. 

 My experiments furnish a new support for the latter opinion, 

 if of course we shall agree to draw inferences as to growth from 

 the weight of the animals. We see that in "thyroid" cater- 

 pillars notwithstanding a considerably decreased weight, the 

 rate of metamorphosis remains totally unchanged. If meta- 

 morphosis were a function of growth, the correlation between 

 the weight of the pupae and the duration of larval life would be, 

 at least in normal conditions, always negative. It is therefore 

 very characteristic that both in the "thyroid" and in the normal 

 material the coefficients of correlation between the weight of the 

 pupae (i.e., the measure of growth) and the duration of the 

 larval period were, it is true, in general rather large, but not 

 always negative (cf. Table V.). According to my opinion we 

 may infer therefrom that between larger growth and quicker 

 metamorphosis of caterpillars there is only the relation of con- 

 temporariness, perhaps dependent on a totally separate, unknown 

 factor (or factors). We have not to do here with real, functional 

 correlation between growth and metamorphosis which could not 

 be abolished even in normal conditions. 



In conclusion I want to remark that the results of my present 

 research are by no means contradictory to my former views on 

 the decisive role of the brain for insect metamorphosis, during 

 normal development (Kopec, '22) as well as during starvation 

 (Kopec, '24). The substance of the thyroid gland from verte- 

 brates may have no relation to the substance (or substances) 

 the existence of which ought, according to my opinion, to be 

 considered as indispensable for the metamorphosis of these 

 animals. I refer their presence in the insect to the presence of 

 brain. The lack of metamorphosis in the caterpillars of Lyman- 

 tria dispar which have been deprived of brain the seventh day 

 after their last moult (Kopec, '22) is sufficient evidence in this 

 connection. The only matter for discussion is whether this 

 influence occurs through the interaction of nerves, or, according 

 to my supposition (not assertion), by means of internal secretion. 

 In recent times Gedroyc ('23) opposed very decisively my 



