618 
MR. W. K. PARKER OK THE STRUCTURE AUD 
marks—truer than the nerves, which are so much specialized,—but even Mr. Balfour 
has not found these in the fronto-nasal region, where there seems to he a rudimentary 
first pre-oral segment formed. 
In the specimen figured, the “amnion” and yolk-sac were removed, but the budding 
“allantois” (all.), as large as the pericardium ( pcd .), was left in situ, and figured. 
That large diverticulum of the “ splanchnopleure,” the pericardium, is a round ball, 
showing through its thin sides the heart ( h .) as a looped vessel, subdividing and filling 
most of the concavity between the arched spine on one hand, and the snout and tail 
on the other. 
r The fore limbs (pt.l.) are oval buds from the infero-lateral edge of the embryo, 
opposite the middle of the heart; the pelvic limbs if rod.) are round buds opposite the 
20th somatome, and embracing the neck of the allantois. 
So that, in this stage, all the embryological machinery is fairly at work, and 
rudiments of all the growing parts and members are already in existence." 
At present, the palatine or sub-ocular visceral fold (mx.p.) is not equal to the 
rudiment of the mandible (ran.) ; but the fold itself, and the oral cleft between it and 
the first post-oral or mandibular fold, both seem to be homologous with the parts behind 
this, the rudimentary mouth. 
Already the mandibular fold is constricted into the shape of an hourglass; the 
lower part, which is very bulbous, and is uniting with its fellow of the opposite side, is 
the future lower jaw; the swollen part above will contain the “quadrate ” or pier of 
the mandible, and the pterygoid bone. 
The next four visceral folds gradually decrease in size, backwards. The first of 
these is the hyoid; the rest, of which the last is imperfect at present, are branchials 
(luy., hr.). 
The hyoid fold lies directly under the rudiment of the ear-capsule; it is broad at 
the top, and is bounded by the first or tympano-eustachian cleft, and by the second 
or hyo-branchial cleft. 
At present these folds are like the rudiments of floral leaves, and form very imper¬ 
fect enfoldings to the newly opened pharynx and oesophagus. 
The “ thalamencephalon,” or fore brain (C 1 ) swells down between the palatine 
folds, but neither the infundibulum nor pituitary body are developed as yet; at any 
rate, the latter is merely the apex of the involution of the mouth. 
In front of the palatine fold the crescentic nasal involution (ol.) is seen, flanking the 
budding hemisphere (C 1 "); over the palatine fold the optic involution (e.) is seen 
folding round the lens. 
* Messrs. Foster and Balfour (‘Elements of Embryology,’ p. 142, fig. 46), have given an excellent 
figure of tbe embryo Chick at the end of the fourth day of incubation, which is exactly mid-way, in 
development, between my first and second stages of Lacerta agilis (Plate 37, figs. 1 and 2). These authors 
give forty “ somatomes ” in their figure; my first has thirty , and my second fifty. For an account of the 
general development of the parts the reader is referred to that work, 
