306 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
appear characters indicating dichotomous divisions of lines of descent, 
the methods of advance along the line of general tendency developing 
in two branches of the group. An example of this is afforded by the 
Odonata and the Diptera ; in one group the specialisation of fore and 
hind wings has followed the same lines, in the other the specialisation 
has resulted in the loss of the hind wings. In both instances a fine 
development of the flight function has been reached. 
Geographical Distribution of Butterflies.* — Mr. H. J. Elwes took 
this subject for his annual address to the Entomological Society of 
London. While pointing out that comparatively little has been done 
by entomologists to show how far the natural divisions of the earth’s 
surface, which have been established for other classes, are applicable to 
Insects, he also points out how little there has yet been done for this 
group. In the first place, we have not as large a knowledge of the 
Insect fauna of many most important areas of which the mammals, 
birds, and plants are well known ; and in the next place, the condition 
of the classification of the Lepidoptera puts serious obstacles in the 
way of any generalisations. He tells us that, though one may be able 
to give the general features of the butterfly fauna in many sub-regions, 
one cannot be sure how far their relative degree of specialisation may 
not have to be modified by future discoveries, and better systems of 
classification based on larger materials for study. 
Metamorphosis of Lepidoptera.j — M. J. Gonin has made a study 
of Pieris brassicse. Each appendage of the imago arises by evagina- 
tion of the hypodermis, previously invaginated. The tracheae are not 
the cause either of the duplication or of the extension of the walls of the 
wing. 
The bud of the wing develops from the earliest larval stage, the 
other organs from the last moult. The antennae, jaws, labial palps, 
and legs of the caterpillar correspond merely to the extremity of the 
homologous organs in the adult. The bud of the leg corresponds to 
femur and tibia in the adult. 
Beside each rudiment a portion of the envelope of the imaginal 
germ persists, another part becomes useless ; the former is regenerated, 
the latter is detached as debris. The hypodermic wall of the thorax is 
partially replaced by imaginal epithelium, that of the head almost 
wholly. 
There is no adherence to twelve imaginal discs in the thorax of 
Lepidoptera ; the dorsal discs of the first segment are wanting ; the 
ventral discs are each represented by several distinct folds. Imaginal 
fold is suggested as a term more appropriate than imaginal disc. These 
folds form new organs, increase existing organs, alter the size and form 
of thorax and head, and sustain the larval hypodermis on the surface of 
the imaginal bud. 
The rudiments of the wings do not participate in the larval moults 
their surface has no cuticle until near the end of the last stage ; 
capillary tracheoles are formed for all the appendages during the third 
larval stage; the permanent tracheae appear at the time of the last 
* Trans. Entomol. Soc. Lond., 1894-5, pp. lvi.-lxxxiv. 
f Bull. Soc. Yaudoise Sci. Nat , xxx. (1894) pp. 89-139 (5 pis., 1 fig.). 
