Miscellaneous. 497 
larva), these cells, on the contrary, separate speedily to a certain ex- 
tent from the adipose tissue in Oligarces (the larva of Pagenstecher 
and Leuckart), although they do not, as Leuckart maintains, constitute 
a true ovary either in Miastor or in Oligarces. In fact, all the cells 
become developed into ova and larvee, and none of them serves for 
the formation of the stroma, for the formation of the envelopes of 
the ova, or for any other analogous purpose. 
In order to explain the peculiarities of these animals, I have en- 
deavoured to establish a theory of the formation and development of 
the ova in the whole animal kingdom, of which the following is an 
abridgemnt. 
The ovum is composed either of a single cell, “the germinal cell,” 
or of the germinal cell accompanied by several other ‘‘ vitelline cells,” 
or by the secretion of the latter, ‘the vitelline mass.’ The ovum 
of the Mammalia, and that of most of the inferior animals, belongs to 
the first category; that of other animals, and especially that of 
Birds, belongs to the second; and that of most Insects to the third 
kind. The “germinal cell’? alone, the nucleus of which is the 
“germinal vesicle,” is subject to the vitelline segmentation which is 
so often discussed. The ‘“‘vitelline cells” and the ‘ vitelline mass”’ 
are not segmented, but pass, without any other form of development, 
into the nutritive vitellus. The germinal cell divides by segmentation 
into minute cells (embryonal cells). A portion of these, not absorbed 
by the formation of the embryo, furnish material for the new ovaries 
and testes, inasmuch as_in general some of the cells form a stroma 
which separates and encloses a greater or smaller quantity of the 
other cells. The remaining non-separated cells form, in Insects, 
what is called the adipose tissue. 
A second element, the semen, is necessary in most animals, to en- 
able the ovum, or rather the germinal cell of the ovum, to develope 
itself; but this stimulus is not always necessary in a great number 
of the inferior animals. The development of the ovum without 
stimulus or fecundation is by no means dependent upon a certain 
more or less advanced point of development of the maternal animal, 
or of its ovary ; for sometimes the maternal animal attains a com- 
plete development even with external and internal genital characters 
(parthenogenesis, as in the bee), sometimes it propagates only in 
the state of a larva without genital characters, and this may be re- 
peated through several generations, either under the same larval 
form (as in our Cecidomyides) or under a different exterior form 
(alternate generations or metagenesis—Trematoda). I by no means 
assume that there is any well-marked limit between parthenogenesis 
and metagenesis; for example, the mode of reproduction in the 
Aphides might be explained in both ways. 
As compared with other insects, I also regard it as characteristic 
that, whilst in general we must make a distinction between the epi- 
thelial and vitelline cells, and the latter serve only for the nourish- 
ment of the embryo, in the present case the epithelial cells serve at 
once as epithelium and as vitelline cells to these larve. 
