64 Miscellaneous. 
Clay near Chippenham, and is described in the Ann. & Mag. Nat. 
Hist. (ser. 2, vol. iv. p. 172), having been previously named by Mr. 
Pearce Ammonicolax longimanus, and considered by him to belong 
to the hermit-crabs. The specimen figured on plate 204 is the 
Meyeria vectensis, Bell (Pal. Soc. 1862, pl. x.), the Meyeria magna, 
M‘Coy. Without any pretensions to be ascientific treatise, the ‘ Note- 
Book of an Amateur Geologist’ must be regarded as a useful, if 
not a necessary, appendage to other geological works, in affording 
a series of accurate sketches of the more interesting geological facts 
and phenomena collected by the author during many years of travel, 
and which, with the accompanying descriptive notes, may be con- 
sidered worthy of being permanently recorded. 
MISCELLANEOUS. 
On the Embryogeny of the Ascidians of the Genus Lithonephria. 
By M. A. Grarp. 
The Ascidian that forms the subject of this note is very common 
at Wimereux on the lower surface of stones. It is very nearly 
allied to Lithonephria complanata, Alder and Hancock, and L. de- 
cipiens, Giard, but differs from the latter in its tadpole, which never 
presents prolongations similar to those of the embryos of the 
Molgule. I believe it to be identical with ZL. eugyranda (Cteni- 
cella), Lac. Duth. ‘The study of its embryogeny is facilitated by a 
physiological peculiarity which is rare in the simple Ascidians: the 
ova are incubated in the progenitive organism; so that we find a 
great number of different stages of evolution in a single individual. 
I have resumed upon this species the investigation of the singular 
productions which issue from the ovum before the segmentation, 
and have received the name of cells of the green layer, or granulosa- 
cells. These observations absolutely confirm those I made some 
years ago upon the ovarian ova of Molgula socialis and several other 
simple Ascidians *. 
The granulosa-cells, without any possible doubt, have an origin 
exterior to the ovule; they have emigrated from the follicle, or even 
from some other part of the ovary, and penetrated very early into 
the vitellus; they are by no means derived from the germinal 
vesicle, which takes no part in this process. The migratory cells 
bury themselves deeply in the vitellus, and may even apply them- 
selves to the germinal vesicle; they are always easily discovered by 
means of very dilute acetic acid. These cells soon become inflated, 
present a distinct wall, and their contents divide into two, four, and 
six protoplasmic masses; then the wall disappears, and these masses 
are by degrees expelled at the surface of the ovum at the moment 
when, the latter being mature, we see the contractions of the 
vitellus commence. ‘The action of acids forwards the expulsion of 
* Association Frangaise, Montpellier, 1879, p. 768. 
