On the 28th of April (fifth day) the embryo has grown so long that it becomes bent in order to accommodate itself to the circumscribed envelope. Now the head, abdomen, and tail are easily distinguishable, and near the head (the larger extremity) small elevations (the rudi of gills and fore-feet) are perceptible. These parts become more apparent by the 30th, when in the concave side of the embryo and toward+ the head n small furrow is seen which &clarets:a the head from the abdomen, and the rudiments of a apino are distinctly visible along its convex border.
By the 2nd of May the position of the embryo is changed, and the tail has already assumed its oar-like form. The embryo begins to move, and its heart may be seen to beat ; colour, too, begins to be present. This appears to be a critical state of the embryo ; for almost half of those of which the development was watched by ltueconi, died at this period or soon after. 3rd May. On one side of the head, and before the two elevations which are the rudiments of the fore-feet, filaments to the number of four on each aide may be observed. 4th May. The changes of position become frequent In that hero presented the embryo shows the lower part of its head and trunk, which is white inclining to green. On the cheat between tho gills of the two aides, where the pulsations of the heart are seen, small irregular blackish spots are obeervable. Before the two claspers are seen also other blackish spots, forming the junction of tho two bands which run along the back, as shown in the preceding figure. The circulation of the blood, which is simple, and performed by a single curved vessel, is seen in the gills, which are of a glassy transparence, and consist only of a single filament without leaflet! WI yet. 5th May. Traces of the eyes may now be just seen ; and the rudiments of the two leaflets are perceptible on the two longest gills. Gth May. The upper small figure shows the young Salamander, seen from above, and of the natural size, just escaped from the envelope. Before its escape, the embryo as it enlarges gradually dilates the envelope, which at last it tears, and so forces its way out. Aa yet the eyes are scarcely defined, though they form two prominences on the sides of the head, and its mouth is so slightly traced that attentive observation is required to detect it ; for it is indicated only by a slight transverse depression beneath the head, and between the two prominences formed by the eyes, and in the middle of the space between the anterior border of the head and the origin of the neck. Its fore-feet begin to separate like buds from the gills, which last are gradually furnished with small leaflets.
very large mouth, whose extremities extend on the sides of the head to the eyee. The head, hitherto narrow behind, hes become much enlarged near the origin of the gills. The two hooks by which the animal anchored itself have disappeared, and the opaque body has become so transparent that the action of the heart and the form and disposition of the abdominal viscera may be observed in the living animal. With this advance ut organisation the sluggishness of the
animal has vanished, and its habits are now manifested. It may i.e seen near the surface, hiding beneath leaves or swimming with rapidity. If, while it floats at rest, a small aquatic insect should pass before it near the surface, it pursues it deliberately, and as soon as it approaches within reach, darts upon it and swallows the prey. Here then we have the little Salamander in the enjoyment of active animal life.
a shows the Salamander in this stage, magnified and seen from below ; Lb are the two prominences formed by the globes of the eyes, and between them is the slight depression which afterwards becomes the mouth ; c, the hook of the right side ; the gills of the sans) side ; r, rudiment of fore-feet of the ammo side ; f represents the same seen in profile, and g the saute Seen from above.
The middle and tuna figure above shims the natural size of the Salamander-Tadpole on the 18th of May, twelve Jaya after its exclusion from the egg. By this time the fore-fmt have become lengthened, and are dividts1 at their extremity like a bicuspid tooth ; thee° two tubercles elongate, and are converted into two toes. Now the eyes are disclosed ; the pupil black, the white speckled with various colours. The yellow back of tho little animal has become green, and the gills are now furnished with leaflets, in which red blood circulates. The transverse depression between the eyes above noticed has become a By the 2Sth of May the Salamander has put on the form above given in the upper figures, seen from above. About this time tho hind-feet begin to appear, and the fore-feet are well developed; these last are, as will be seen, long in proportion to the trunk. The following are the principal points manifested under the microscope in this stage :-1, two small eminences or excrescences, extending from the exam to the abdomen ; 2, the parietes of the abdomen take the colour of the insects on which the animal feeds ; 3, the changes of colour from yellow to green, during the growth of the tadpole, are purely accidental, and commence immediately on the escape of the animal from the egg ; 4, the inner toes first push forth, and this holds good also with regard to the hind-feet ; 5, the atnylaecoue bone of the organ of hearing is now formed, and may be seen through the skull and skin ; 6, at this period, and even sooner, the animal begins to expel air from the mouth. The two lower cuts show the same 'salamander on tho 12th Juno ; the small figure represents it of the natural size and as seen from above, and the larger figure tnag nified and in profile. Now time hind-feet have almost attained their development, though the fifth toe Li/wanting. The lungs extend about hallway down the trunk, and are visible through the parietes of the abdomen. The longest gills, which were furnished with only 13 or 14 leaflets] 13 or 14 days previously, have now nearly 20.