1908-9. | THE Hapits OF PLETHODON CINEREUS ERYTHRONOTUS. ’ 481 
Larvag.5 mm. Figure 9. 
The eye is now pigmented. ‘The mouth is well defined and the gular 
fold projects a little over the base of the gills; these now appear as three 
points on a cotumon base. The anterior limbs have a length of .5 mm. 
the posterior of .25 mm.; the latter are now attached on the line between 
yolk and body, consequently the anus lies in the free part of the body 
posterior to the yolk. 
The accumulation of fluid between the egg and the innermost envelope 
has increased the diameter of the egg and envelopes together from 4.5 
or 5.5 to 6.5 or 7mm. ‘This is not due to a thickening of the walls of 
the spheres but to such a distension of the inner one that yolk and larva 
together occupy only the lower two-thirds of the cavity. No further 
enlargement of the cavity occurs, consequently the larva becomes more 
and more closely coiled as its length increases, for the diminution of yolk 
that soon becomes noticeable does not compensate for the increased bulk 
of the larva. 
The rotation ascribed to cilia on the ectoderm has been noticed in 
some larve of this Stage of development, but in none later. 
Although the blood is not yet red a hand lens will reveal the follow- 
ing plan in the circulation over the yolk miass, the vessels appearing as 
colourless lines against the white background of the yolk; the direction 
of flow can be followed as the corpuscles are easily visible. Small arteries 
metamerically arranged run laterally over the yolk; they branch and 
anastomose in such fashion that a network two or three meshes in width 
is formed between the margin of the body above and the vein in which 
they terminate ventrally. (Figure 9). Usually there are two such 
veins at first, a right and a left; at a variable time in later development 
one disappears, as is usual in Urodeles. Sometimes the anterior part 
of the network on one or both sides collects into a separate vein, making 
for a time three or four separate trunks that unite just posterior to the 
heart. Sections show these vessels all lying, as might be expected, in 
the splanchnic mesoblast which has ere this completely surrounded the 
yolk. 
Larva 10.5 mm. 
At about this length sections show for the first time perforation of 
the gill pouches, two only—the first and second—ever become perforate. 
The anterior limbs show the first indications of digits in that their extremi- 
ties are flattened and show a terminal notch and a shallow groove leading 
to it on each side. The posterior limb is not appreciably flattened. 
