476 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vor. VIII. 
the innermost sphere increases markedly, thus relieving the growing 
embryo from pressure. 
The eggs vary from 3.5 to 4.5 mm. in diameter. In many of those 
bunches which contain several eggs there is one egg considerably smaller 
than the others; with this exception there is: great uniformity in the size 
of the eggs of the one cluster. The considerable variation noted above 
exists between the eggs of different clusters. 
The colour of the egg is a very pale yellow, a tint due to the yolk 
for no pigment is present. The upper part of the egg being the more 
free from yolk is almost white. Variation exists in the tint of the eggs 
of different clusters, the range being between very pale cream and light 
orange-yellow. 
The usual rotation of amphibian embryos in their earlier stages 
occurs also in Plethodon but is modified by the large amount of yolk 
present. In the usual type of amphibian embryo, such as Ambly- 
stoma or Rana, the amount of yolk is not so great as to render it impos- 
sible for the embryo to turn over when the course along which the ciliary 
movement urges it sodemands. Until the Plethodon embryo has reached 
a length of 6 mm. it lies along a meridian of the yolk mass and a true 
forward movement would require the yolk at times to be uppermost. 
Whether because the ciliary movement lacks force to drive it into this 
position or for some other reason less obvious the rotation that occurs 
is around the vertical axis. There is no uniformity of movement even 
in eggs of the same bunch; an occasional one will be motionless and the 
others about evenly divided between motion to right and motion to left. 
A little later when the embryo twists itself into the horizontal plane the 
appearance in rotation is that of the ordinary amphibian embryo but 
the same lack of uniformity of direction obtains, some few embryos will 
not be moving at all, of the rest the head will be preceding in some cases 
but the tail in quite as many others. This latter direction was not ex- 
pected and caused an examination of Amblystoma eggs to be made sub- 
sequently to determine if anything comparable was to be found there. 
Eycleshymer (’95) notes an early irregularity of direction but this is not 
the impression derived from a brief examination of larve in later stages; 
nor is it to be expected from the account of the ciliation of Rana and Triton 
larve given by Assheton (’96). The stage of developement of Ambly- 
stoma equivalent to the one of Plethodon in which the backward move- 
ment is so marked is that in which the gills are beginning to appear and 
the larva is curved laterally in a semicircle to accommodate itself to its 
spherical envelope. At this stage nearly all embryos examined will be 
