1885. | Entomology. 175 
arising first; and the body becomes segmented, the head having 
three (afterwards four) segments ; the thorax three and the abdo- 
men seven or eight (afterwards ten, including the telson). Thus 
seventeen would be the maximum number of somites of the in- 
sects. 
9. Alimentary Canal—An invagination for the mouth is seen 
(stomodeum, st), and subsequently another for the anus and in- 
testine (proctodeum, prc). These meet each other in the body 
so as to complete the alimentary canal. The stomodzum forms 
cesophagus and stomach ; proctodzeum forms intestine and rec- 
tum. The mid-intestine is not chitinized, but this is related to 
its function and has no embryological significancy 
he true endoderm becomes yolk-balls, afterwards wandering 
cells, subserving nutrition, but not directly aiding in the forma- 
tion of the alimentary canal or of any other organ. The author 
excludes the endoderm from any share in forming the intestine 
in all Aithropods, if not more widely. 
10, The appendages now shew their special characters. They 
arise by an evagination of the body wall, including ectoderm, 
mesoderm and part of the body cavity. Thus arise the mandi- 
bles and two pairs of maxilla in the head; these keep small as 
compared with the limbs ; the mandibles and first maxillæ after- 
wards combine to form a retort-like mass. The antennz arise 
beside the stomodzum, in the same way as the other appendages 
(not from the procephalic part). The EENEI segments bear 
pote si AARIN probably rudimentary lim 
The procephatic part is not originally lobed i in Aphides; it 
ation as an extension forwards of the antennal segment. It sub- 
sequently becomes pointed and forms the labrum. 
12. The ventral nerve-cord arises from the ectoderm, its cells 
dividing so as to leave only a thin dermal layer. Transverse seg- 
mentation causes it to be marked off into ganglia (three anal, 
three thoracic, seven abdominal, which are small). These subse- 
quently coalesce into a subcesophageal and ventral mass 
The érazn is formed in the region of the lateral oni but its 
primitive relation to the ventral cord was not made o 
I ody-cavity—The general body-cavity wea ao the orig- 
inal segmentation-cavity. In an early stage free polar-cavities are 
formed between blastoderm and yolk, thus corresponding to the 
segmentation-cavity of lower animals. These cavities uniting 
insert themselves between the yolk and germ-streak, and extend 
into the embryo and its appendages. The same cavity spreads 
under the serous layer as a separate cavity. In the early stages 
the embryo is open dorsally, and by this route the pseudo-vitellus 
and generative mass find admission to its interior. Between the 
embryo and amnion is an “ embryonal cavity” derived from the 
lumen of the ovarian tube. 
14. Revolution of Embryo.—When the parts of the body and 
