206 — PROF. HUXLEY ON THE AGAMIC REPRODUCTION 
open close to the vulva. They consist of a delicate etmuerarciess coat lined by a thick 
layer of granular substance, whose cellular composition is very indistinct in the fresh 
state, but becomes obvious on the addition of acetic acid. 
‘The interior of the gland contains a clear, viscid, strongly-refracting substance, appa- 
rently separated from the epithelial lining by a membranous layer. I am in doubt, 
however, whether this apparent membrane be anything more than the folded and wrinkled 
outer layer of the viscid matter. When the Aphis is suddenly placed in glycerine or 
subjected to slight pressure, a drop of the colleterial secretion not unfrequently exudes 
and manifests its viscidity by leaving a long trail. 
The fully-formed ovum (Pl. XL. fig. 1, F) measures about th of an inch in length. It 
is oval, rather smaller anteriorly, and of a deep green hue, in consequence of the colour of 
the yelk. The chorion is a tough transparent membrane, about 5555th of an inch thick, 
and presents no external sculpturing or internal structure. Internal to the chorion is 
a delicate vitelline membrane which immediately invests the yelk. It is, however, con- 
nected with the chorion posteriorly. When the egg is heated with caustic potass, the 
yelk is driven away from the sides (eventually dissolving), and with it the vitelline 
membrane on the sides and at the anterior part of the ovum; posteriorly, however, I 
always found it adherent. The yelk itself is very coarsely granular ; so that there would 
be no chance of discovering the germinal vesicle, even if it existed. 
The recent observations of Leuckart and Meissner on the micropyle of the ovum in 
Insects naturally induced me to look for such a structure in the egg of Aphis. 
Leuckart, in his elaborate essay, clearly shows that the micropyle may be single or 
multiple, and may occur at either or both poles of the egg; but unfortunately he gives us 
less information respecting the ova of the Homopterous Hemiptera than regarding those 
of any other great group of Insecta. Cercopis, in fact, is the only genus of this division 
in which he has observed the micropyle with certainty, and here there are two, one on 
each side of the anterior pole. 
: The anterior extremity of the chorion in Aphis (Pl. XL. fig. 4, B) presents a small 
conical papilla, in which I have been unable to discover any aperture. Internally, how- 
ever, the corresponding surface of the chorion appears as it were rough and uneven ; and 
when caustic potass is added, it, like the rest of the inner surface of the chorion, exhibits 
a vay curious marking, as if so many circles or more irregular figures were impressed 
: upon it The thickness of the papilla is about Zvooth of an inch; and in young ova å 
delicate filiform appendage more than once appeared to be continuous with it: this, how- 
ever, was invariably absent in fully-formed ova. 
At the opposite pole (fig. 4, A), the ovum presents a curious appendage, about s$oth of. 
seg in length. When the ovum is in its natural position within the ovary, the 
= "e E eg which closes over it below, leaves a sort of chamber in which this 
VE så tp d I fees closely applied against the chorion, is received. lu 
3 er inh st appendage appears like a rope with loosened strands, 
M ibd assi xs and is seen to be coated with a clear gelatinous substance, 
hadde ER es rod- ike filaments of about zygth of an inch in length are ım- 
: . caustic potass, this clear substance and its imbedded particles are 
