209 
- mixed with the bran and dried up into a lump. Such wounded 
pupae do not develop into beetles, but die sooner or later in pro- 
portion as the wound occurs on more or less vital organs. 
The cause of these injuries is alike a beginning of gnawing by 
the larvae, from which the young pupa has been able to withdraw, 
as it always reacts to mechanic stimulation with vehement move- 
ments. 
The gnawing away may, especially in young pupae, be so far 
advanced that only small remainders of the chitin-shell are found 
back. 
Between these extremes one finds many intermediate stages of 
mutilation. 
With this, the mortality among the pupae is not yet at an end. 
The pupa has still a critical period to pass through, viz. the time 
shortly before casting the pupal moult. Some unknown disturbance 
or other during the metamorphosis either occasions its death, or 
prevents a normal beetle from emerging. 
The disturbance usually manifests itself in that the wings are 
defective, or are not perfectly developed, and that the pupal moult 
in the distal part of the body is not removed. The legs are mostly 
developed so far that these pseudo-beetles can utilize them yet. They 
are wretched animals, which crawl about needy and invalid, and 
die after a short time. 
They have been mentioned separately as “half beetles’ in ourmorta- 
lity lists. The mortality of pupae gathered in the years 1915/1916—- 
1916/1917 and 1917 is shown in the table below. 
Pupae Of the a aaa Mortality of Pupae in 9p. 
athered. as | as as SEE} 
5 pupae | halfbeetles| pupae | halfbeetles Total 
1915—1916 8331 1269 150 15.2 %/ | 1.8 0 17 0/0 
1916—1917 28138 9355 1665 33.2 5. 30° 5 
1917 8135 1617 201 LOSS | 24 i 22 
Eee. | + 78 Ns 28 ee 
Total and averages | 44604 12241 | 2016 27.4 0/0 4,5 0/9 31.9 0/9 
More than once already I had been struck by the fact that if I 
laid big pieces of rusk, soaked with water, in the larvae jar, the 
larvae greedily eat of them. This fact led me to the supposition 
14 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
