450 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
“ They are the differentiations into two different directions from a 
common starting-point, the initiating factor for this divergence being 
the relative differences of the levels of the primitive sense-areas, in 
reference to the level of the surrounding skin.” 
a. Insecta. 
Eyes of Caterpillars and Phryganid Larvae.*— Herr 0. Pankrath 
has examined the eyes of the caterpillars of Gastropacha rubi, and of the 
larvae of the Phryganida. As is well known these eyes do not, as a 
rule, survive in the adult, for they disappear during the pupal stage, and 
are replaced by perfectly new organs. It may be supposed, a, priori , 
that tbe same components are found in both sets of eyes, and a simple 
eye of a larva may well be compared with a facet of an adult’s eye. 
This facet consists of a cornea-lens, a crystalline cone, and a retinula, 
which, as a rule, consists of seven parts ; there are just the same com- 
ponents in the eye of a caterpillar ; the fact that there are also seven 
rods in the retinula is probably not an accident, but indicates the close 
connection between the two kinds of eye. 
Notwithstanding this resemblance there is a great difference in the 
vision of the caterpillar and the butterfly. In the latter a number of 
facets act in conjunction, and the eye is adapted for the perception of 
movements; in the caterpillar each eye acts independently, and is 
rather adapted for the perception of bodies. The powers of such an eye 
are, in consequence of the small number of nerve-endings, very small, but 
it is probable that they can do more than distinguish between light and 
darkness, and are able to perceive bodies, though not to distinguish them. 
Intermediate stages can be easily detected between the two extremes ; 
if the eye of a caterpillar be more closely approximated and covered by 
a continuous cornea, we get the eye of the Phryganid larva ; while, if 
the separate eyes in this organ be multiplied and set closer together, we 
get the facetted eye, for this last is nothing more than a complex of a 
number of separate eyes. 
Diminution in Weight during Pupation.f — Herr F. Urech shows, 
by means of curves, the gradual diminution of weight throughout the 
pupal stage of Pieris ( Pontia ) brassicse. The various curves express the 
influence of the different temperatures at which the pupae were kept, in 
the open air or within doors. They show very vividly that the weight 
• diminishes with great rapidity towards the end of pupation, and also 
that dry air shortens the length of the period. Tbe loss is of course 
due to the internal metabolism of the pupal reconstruction which goes 
on without recuperative income. Of the water given off along with 
carbonic dioxide, part is directly associated with the continual oxidation, 
the rest forms a large proportion of the secretion exuded before the 
emergence of the imago. Herr Urech also gives a table showing the 
rapidity with which the wings grow after emergence. 
Tracheal Endings in Sericteria of Caterpillar s.} — Hr. C. v. 
Wistinghausen has investigated the mode of termination of the tracheae 
* Zeitschr. f. Wiss. Zoo]., xlix. (1890) pp. 690-708 (2 pis.). 
t Zool. Anzeig., xiii. (1890) pp. 254-60. 
X Zeitschr. f. Wiss. Zool., xlix. (1890) pp. 565-82 (1 pi.). 
