DEVELOPMENT OF THE SKULL IN THE LACERTILIA. 
617 
Turtle are manifestly Chelonian ; and those of the Mole have their fore-paws very 
large, and lying on each side of the skull. They could be mistaken, even at that early 
stage, for the embryos of no other Vertebrate.* 
My smallest embryo of Lacerta agilis (Plate 37, fig. 1), is, if anything, a little less 
developed than the smallest embryo of the Snake (“ Snake’s Skull,” Plate 27, figs. 
1,2); thut, rather, would answer to the second stage of the present paper (Plate 37, 
fig. 2). 
I am careful to give all these details minutely, so that a harmony may be made of 
these early conditions in various Vertebrata; my stages are quite arbitrary, answering 
to my materials. 
Even in so small an embryo as my youngest (Plate 37, fig. 1), the organic processes 
have been busily at work, and the main parts are already to be seen in rudiment. 
The head is very large, relatively, and the “ cephalic flexure ” is perfect, throwing 
the mid brain (C 2 ) outside the line of the general curve of the embryo. 
That, and the fore brain (C 1 ) are nearly of a size, but this vesicle sinks down 
between the eyeballs, and is not so apparent: moreover, the hemispheres are budded 
from it in front and are seen as a pair of swellings; the optic vesicles, also, have grown 
from the fore brain, and are shielded by a fold of skin. 
The hind brain (C 3 ) is longer than the others, it is also narrower, less convex, 
being somewhat crested above, and sub-lobulate; it is, however, larger than it seems, 
being hidden between the right and left hind face. 
The whole embryo forms nearly a circle, the tail almost touching the head ; the two 
regions, head and body, are about equal in length, but in bulk the head greatly 
preponderates. 
There is much invaluble knowledge to be gained for morphology in a germ like this, 
without dissection, and I shall, without poaching on the embryologist’s preserves, 
gather what I want from the outside of his subject; in a further stage (the third) I 
shall join hands with him on the headland which is common property. 
In the parts that belong to the head, segmentation is indicated most clearly by the 
clefts formed in the sub-ventral region of the sides; behind the head, the divisions 
between the “ somatomes ” are evident in the sub-dorsal region ; of these, at present, I 
can count about thirty. 
At present, by the help of the clefts, I can only find six visceral folds or cephalic 
segments; the last of these is imperfect, and one more, in front of the face, appears 
afterwards. 
These are all there will ever be, and the last, or seventh, is aborted long before the 
embryo is ripe ; as for segments, such as those in the body, which are indicated by 
the evident “ muscle-plates,” two, or at most three, can be found in each side of the 
notochord, in front of the first vertebra. 
The “ head cavities ” will be treated of in the third stage; they are invaluable land- 
* It is beyond nay province to explain this fact; I leave its interpretation to others. 
4 £v 2 
