ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 65 
more than half the length of the body, and constitutes the well-known 
proboscidi form “labium” of the -lp/zs.2 
The thoracic members or legs have elongated so much, that their 
terminations ate bent inwards, to allow of their lying within the 
pseudovitelline membrane. Their characteristic subdivisions are 
indicated ; and the terminal claws are beginning to be formed. 
From this size up to that at which the larve are born (Pl. XX XIN. 
[Plate 4] fig. 4) (when they are less than jth of an inch in length), 
the principal changes are the following:—The appendages as com- 
pared to the body, and the latter as compared to the head, undergo 
great elongation. The anterior pair of thoracic limbs and its somite, 
the prothorax, come into very close contact with the head, so that 
the cervical separation becomes obsolete, or is only indicated by a 
groove. The labrum and labium acquire their characteristic form 
and proportions ; and the mandibular and maxillary seta elongate, 
and take their final position. 
The “siphons,” so characteristic of the genus, appear as obtuse 
tubercles on the dorso-lateral region of the fifth abdominal somite. 
The little larva exhibits unequivocal signs of life, but still remains 
enclosed within its pseudovitelline membrane, to which another trans- 
parent and structureless envelope, fitting the body of the larva and 
all its limbs as a loose glove fits the hand, seems to have added itself. 
This second coat is, in fact, the embryonic integument, which is now 
being cast; so that the creature must undergo its first ecdysis either 
before, or immediately after, it is born. The head assumes its normal 
proportions. The corneee become facetted ; and the pigment increases 
greatly in amount, assuming the form of an oval deep-red patch. 
The clypeus and the procephalic lobes unite, but readily give way 
when the head is crushed, and allow of the exit of the cerebral mass, 
which has in the meanwhile been produced by a differentiation of the 
inner substance of the procephalic lobes, just as the other ganglia are 
the product of the blastoderm of their somites. 
If the account of the development of the external organs of Aphis 
which I have just given be compared with the statements of Kélliker? 
and Zaddach,? it will be found that there is a close correspondence 
in all essential respects between the embryogenic phenomena of at 
least three orders of /wsecta—the Hemiptera, the Diptera, and the 
1 Zaddach considers, from his observations on Phryganea and other Insects, that the 
labium is the product, not of confluent maxille, but of an outgrowth of the sternum by which 
these are supported, the maxille remaining as the labial palpi. I do not deny that this may 
be the case in /Azs; but I have been unable to find positive evidence of the fact. 
2 De prima Insectorum Genesi, 1842. 
3 Die Entwickelung des Phryganiden-Eies, 1856. 
VOL. II i 
