w 
Fig. 5. Sacs of A: pond larva (young, 5 mm.) and B lake larva (full grown) to show 
die relative thickness of the different parts of the walls. A enlarged ca. 250 diam. 
(Leitz obj. 6, oc. 1), B ca. 100 diam. (L. obj. 3, oc. 4); camera lucida. A^ and in B 
indicate the ends of the tracheal trunks originating from the sacs. 
3 
Vidensk. Meddel, fra Dansk naturh. Foren. Bd. 07. 
