THE AMERICAN LOBSTER. 
215 
Cut 39 represents a median longitudinal section through, the embryo shown in 
fig. 230, plate 51. Here the entire embryo is immersed in the yolk or in a thin coagulable 
fluid derived from it, through which it can be seen, while the cell plate touches the 
surface in a narrow, bow-shaped area, but dips below again at its peripheral margin. 
The cell plate beyond the confines of the thoracic-abdominal process and appendages 
of the embryo consists of a single layer of very large cubical or columnar elements 
gorged with yolk. In front and behind, the edges of this sheet unite to form a cul-de- 
sac, so that the whole structure resembles iu form a flattened bag, which is partially 
buried in the yolk, with which it communicates by the opening or mouth of the sac 
below. The edges of the plate are curled over in the yolk, like one of the limbs of 
Cut 39. —Median longitudinal section through ab- 
normal embryo shown in fig. 230, plate 51. Fixed 
with picro-sulphuric acid, stained in Kleinenberg’s 
hsematoxylon, August 9, 1892. 
AbP, thoracic-abdominal process. Deg., egenerating cells, 
of stomodaeum. Pit, pit formed by ingrowing fold, r, outward 
y., food-yolk, abnormally covering embryo in cut 39. 
Cut 40. — Sagittal section through abnormal em- 
bryo in early stage of development. Fixed in 
picro-sulphuric acid, stained in Kleinenberg’s 
hmmatoxylon, August 9, 1892. 
, ep.f., ingrowing fold of surface-epithelium. Mo, mouth 
fold of surface epithelium, y.c., scattered cells in yolk. 
the letter S. In other respects the histology of this egg-nauplius embryo resembles 
that of a normal form, except in perhaps a great preponderance of degenerating cells. 
In the embryo, the surface view of which is shown in fig. 22S, plate 51, essentially the 
same conditions are seen. These abnormal embryos which have just been described 
are due in all probability to a disturbance of the normal mechanical conditions under 
which the egg usually develops. It is quite probable that they could be artificially 
produced, but no experiments have yet been made in this direction. 
I have noticed another interesting abnormal variation in the invagination stage. 
(See 91 ). At a period nearly corresponding to that shown in fig. 255, plate 51, there 
is a large irregular cavity or several communicating cavities in the depths of the egg. 
This chamber contains very little yolk, and its wall is composed of cells which grasp the 
