62 ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 
Dorsally and posteriorly, the rudiment of the head is originally 
continuous with the thoracico-abdominal thickening ; but a separation 
early takes place at this part, and the interval is occupied by the 
pseudovitellus, which here comes into immediate contact with the 
pseudovitelline membrane. 
In an embryo ;45th of an inch in length (Pl. XX XVII. [Plate 2] 
fig. 5), this interval has increased so much, that the cephalic blasto- 
derm does not extend on to the dorsal region at all, but lies 
almost flat under the pseudovitellus, in the anterior half of the 
ventral region. 
In embryos 715th of an inch in length (Pl. XXXVII. [Plate 2] 
fig. 6), I have found the cephalic portion of the blastoderm beginning 
to extend upwards again over the anterior face of the germ, so as to. 
constitute its anterior and a small part of its superior wall. 
This portion is divided by a median fissure into two lobes, 
which play an important part in the development of the head, 
and will be termed the “ procephalic lobes.” I have already? made 
use of this term for the corresponding parts in the embryos of 
Crustacec, 
The rudimentary thorax presents traces of a division into three 
segments ; and the dorso-lateral margins of the cephalic blastoderm, 
behind the procephalic lobes, have a sinuous margin. 
It is in embryos between this and ;23,th of an inch in length that 
the rudiments of the appendages make their appearance ; and by the 
growth of the cephalic, thoracic, and abdominal blastoderm, curious 
changes are effected in the relative position of these regions. 
_ In embryos about ;3,th of an inch in length (Pl. XX XVIII. 
[Plate 3] fig. 1, Ia), the procephalic lobes are so completely bent 
backwards as to lie close against the tergal surface of the rest of the 
cephalic blastoderm, so that no pseudovitelline granules can any 
more be seen in this region of the body. At the same time the 
lobes have enlarged, and extend back as far as the base of the fourth 
pair of visible cephalic appendages. Their infero-lateral angles are 
rounded and produced, forming an elevation which appears to be 
the rudiment of the eye. 
Below the anterior extremity of the embryo, the blastoderm is 
produced on the median line into a tongue-like process (6), whose 
inferior part eventually becomes the labrum, while superiorly it sends 
a triangular process (the rudiment of the clypeus) into the interval 
between the procephalic lobes. 
Immediately behind the labrum, the blastoderm curves at first 
' “Lectures on General Natural History,’ Med. Times and Gazette, 1856-7. 
