160 
MR. W. K. PARKER ON THE STRUCTURE AND 
pouch that projects from the ventral aspect of the embryo. The fore limbs are large 
flat buds behind the middle of the larviform embryo, and the hind limbs are much 
smaller and are curved inwards on each side of the rudimentary tail. The meso- 
cephalic flexure is well marked, and the cerebral vesicles very large; the long, 
lobulate hind-brain is covered with a very thin layer of tissue. The pineal elevation is 
to be seen between the fore- and mid-brain, and the fronto-nasal process against the 
former vesicle. Between these parts the notch which contains the rudimentary 
olfactory organ is seen ; this is bounded, above, by a band which runs into the large 
maxillo-palatine lobe. This lobe is separated by a sharp notch, the oral opening, from 
the rudimentary mandible, behind which is the hyoid fold, and the first branchial fold ; 
these are separated by clefts. 
Over the maxillo-palatine lobe the small eye-ball is seen, and over the hyoman- 
dibular cleft the oval auditory sac. 
Second Stage.—Embryo of Mole, ^ inch long. 
I have had sections'"' made of the embryos at this stage; these have been studied, 
but not figured, as the tissues of the skeleton were in an indifferent state, and it is not 
part of my plan, as a rule, to give histological figures, 
The external form, however, in this stage is very important (Plate 16, figs. 2-4), as 
the influence of heredity, which had begun to show itself in my first stage (fig. 1), in 
the large size of the rudiments of the fore limbs, is here very evident indeed. 
The limbs are now, evidently, pentadactyle ; but the fore limb is also very large, 
and close to the head. 
The folds of the outer skin are now perfecting themselves, we see the eye-ball 
in its circular setting, the external meatus of the ear is formed, and the outer 
nostril, with its rim complete. 
Third Stage,—Embryo of Mole, 7-| and 8 lines long. 
In an embryo two-thirds of an inch long (Plate 16, fig. 5) the fingers and toes are 
distinct, and the small pig-like creature has got a distinct circular eyelid ; the meatus 
externus is very small, and encircled with a fold, and the nostrils are now well 
fashioned. 
The true hyaline cartilage is now differentiated, and in this stage I shall give a 
description of the sections made from a specimen scarcely two-thirds of an inch 
(7-| lines) long. The dissected figures of the skull of the next stage (f inch long, 
Plate 25, figs. 2, 3) will serve, like a ground-plan, to explain both the sets of sections, 
namely, those of the same stage, and those of this earlier embryo. 
From about 200 exquisitely sectioned and perfectly stained slices of this small 
* These and most of my sections were made for me by my son, Professor W. N. Parker ; those of the 
next stage were made by, and belong to, F. Penrose, Esq. 
