144 EDUARD UHLENHUTH 
Exactly the same phenomenon can be seen in a group of Punctatum 
(Group P 1916) maintained at a high temperature, such as 
the development of definite characteristics of a metamorphosed 
animal during the larval stage. In this case the yellow network 
was separated into yellow spots during the larval stage—a 
phenomenon which does not occur in the case of the worm animals 
before they have left the water. 
From what has been stated above we can see that even in those 
animals which metamorphosed first and, in the series of Opacum 
larvae (O 1916) fed with equal quantities, metamosphosed 11 
weeks earlier than the worm animals, the process of metamor- 
phosis was disturbed. This becomes much more apparent. if 
for the date at which the first animal underwent metamorphosis 
we substitute that of the last animal metamorphosed. In that 
case we obtain the following relationship: In the series of Opacum 
larvae (O 1916) after 32 weeks have passed, 12 per cent of the 
thymus-fed animals are yet in a larval stage, whereas the worm- 
fed individuals all had metamorphosed as early as the 29th week. 
Thus, the period of metamorphosis in the worm series extended 
only over 5 weeks, whereas in the case of the thymus animals 
it has already lasted 19 weeks. In the repeatedly mentioned 
group of A. punctatum larvae (P1916) kept at a high tempera- 
ture, the last thymus fed animal had not left the larval stage 
even after 8 months, whereas the last worm-fed animal had 
metamorphosed after only 53 months; thus in the worm-fed 
animals, metamorphosis covered a period of only 23 months, 
whereas in the thymus animals it lasted 5 months. In a group 
of A. punctatum (P 1916 C) kept at a low temperature, a worm- 
fed series comprising individuals which out of a number of 300 
larvae had not yet undergone metamorphosis was added to a 
thymus-fed series which had been under observation for about 
5 months. In other words, this worm-fed series consisted of 
larvae which were abnormally late in undergoing metamorphosis. 
The first of these worm-fed animals left the water 5} months 
after hatching, the last 72 months after hatching, the period of 
metamorphosis extending in this series over 2 months. Of the 
thymus-fed animals the first metamorphosed after 43 months, 
