484 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vov. VIII. 
in his larvee Montgomery (’o1) was led to suggest the possibility of 
their development before the anterior limbs, contrary to the usual con- 
dition in Urodeles. This proves not to be the case, though they do appear 
earlier than usual and grow more rapidly. 
The development of gills is retarded. No trace of them as separate 
points is found until the larva reaches a length of 8 or 9 mm.; in Am- 
blystoma the same occurs at a length of 6mm. Looking at limbs and gills 
together the contrasts are marked; when Plethodon first shows external 
gills its posterior limbs have been for some time distinct; when Ambly- 
stoma first shows posterior limbs its gills are 1.25 to 1.5 mm. long and 
plentifully branched. 
It is of general occurrence that the gills of such amphibian larve 
as have no free aquatic life are proportionately longer than those of larve 
that do. The condition in Salamandra atra as described by Chauvin 
(77), shorter and stouter gills being assumed when aquatic life was forced 
on the larva, is typical. ‘This obtains also in Plethodon, the filaments 
as well as the main trunks of the gills being much longer but much less 
numerous than in aquatic larvee of the same size, e.g. those of Amblystoma. 
Such marked reduction in the number of filaments does not occur among 
all Urodele larve of non-aquatic development. In aquatic larve the 
gills are largely directed backward to afford as little resistance as possible 
to passage through the water; in Plethodon they spread out as widely as 
possible, the direction being a matter of indifference. The point of im- 
portance is that they apply themselves to as much of the mucous envelope 
as possible and so place themselves where they can best obtain a supply 
of oxygen. 
Plethodon has neither the balancers nor the adhesive discs common 
among other amphibian larve. / 
The body of a Plethodon larva is from the first that of a terrestrial 
animal, cylindrical and without trace of median fins. Like the larva 
of Autodax (Ritter and Miller ’99) it has lost the swimming instinct; 
when placed in water it sinks to the bottom and falls on one side; often 
indeed it twists its body and writhes violently but such movements never 
result in any progression or even in temporarily regaining balance. They 
seem to be only the wriggling that occurs periodically within the egg 
envelopes; it can always be induced by any stimulation of the larva. 
The complete darkness in which the development of Plethodon 
takes place is partly responsible for peculiarities in colouring. Pigment 
is entirely lacking in the egg nor does it appear in the larva until a length 
