ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
711 
Closed Tracheal System in Insect Larvae.* — The late Dr, H. 
Dewitz was engaged on some observations on the closed tracheal system 
of larvae, the chief results of which may bo thus summarized. In the 
young stages of the Odonata and Ephemeridse there is an open tracheal 
system, and in some of the families thoracic stigmata are seen at a very 
early stage. Mature nymphs of iEschnidae, Libellulidae, and Agrionidae 
were found to be able to inspire as well as expire air by the stigmata. If 
all the gill-lamellae of young Ephemerid larvae are cut off, the animals 
undergo ecdyses in which gill-lamellae are newly formed. 
Insects Accepted or Rejected by Birds, f— Mr. A. G. Butler has, 
this year, continued his experiments with insects and birds. He is 
convinced that the tastes of the latter not only differ in individuals of 
the same species, but that the same individuals in consecutive years vary as 
to their likes and dislikes ; the largest British spider is not an object of 
fear to any insectivorous bird ; the imago of Abraxas grossularia is far 
from being distasteful, although the larva is distinctly so to many, if not 
all, insect-eaters. Neither caterpillars nor birds have the same notions 
of beauty as human beings. Mr. Butler’s observations do not afford 
much support to some recent speculations as to protective coloration. 
Evolution of Bristles, Setae, and Tubercles of Caterpillars.^ — 
Prof. A. S. Packard has a paper, full of observations, in which he brings 
together hints as to the evolution of the bristles, spines, and tubercles of 
certain caterpillars, which appear to result from a change from low- 
feeding to arboreal habits ; these are illustrated by the life-histories of 
some Notodontians. 
He comes to the conclusion that the more prominent tubercles, with 
the spines or bristles arising from them, are hypertrophied piliferous 
warts ; the warts with the seta or hair which they bear being common 
to all caterpillars. The hypertrophy or enlargement was probably due 
in the first place to a change of station from herbs to trees, involving 
better air, a more equable temperature, and perhaps a different and 
better food. The enlarged and specialized tubercles developed more 
rapidly on certain segments than others, because the nutrii nt fluids 
would tend to more freely supply parts most exposed to external stimuli. 
These last were largely due to the visits of Insects and Birds, and the 
result was a mimicry of the spines and projections on the trees ; the 
colours were due to light and shade, and the general result was protective 
mimicry or adaptation to tree-life. 
The cause of the hypodermic cells at the base of the spmes of some 
forms becoming specialized to secrete a poisonous fluid is not yet known. 
After primitive forms, members of different families, had become 
established on trees, a process of arboreal segregation or isolation would 
set in, and intercrossing with low-feeders would cease. Heredity would 
cause a succession of generations perfectly adapted to arboreal life, 
while natural selection would constantly tend to preserve new varieties, 
species, and genera, and would not cease to act in a given direction, so 
long as the environment remained the same. Prof. Packard is of 
opinion that the first steps in the origination of a species, genus, family, 
* Zool. Anzeig., xiii. (1890) pp. 500-4 and 525-31. 
t Ann. and Mag. Nat. Hist., vi. (1890) pp. 324-7. 
X Proc. Boston Soc. Nat. Hist., xxiv. (1890) pp. 494-560 (2 pis.). 
