8 
from chromatophores. A number of chromatophores are observed 
directly over the lens. They have extended to the base of the gills, 
although but few are seen in the gill bars. A few are present in the 
dorsal surface of both the. anterior and posterior limbs. The dorso- 
lateral veins extending along the dorso-lateral surface of the yolk are 
now clearly defined. The chromatophores are more densely aggre- 
gated along the lines of these veins, so that they form a fairly well 
defined band extending along either side. 
In the decapitated larvae of this stage the distribution of chro- 
matophores is in general the same as in the normal, yet owing to 
their contracted condition the larva is on the whole not nearly as 
dark as the normal. 
Larvae 19-20 mm. The most notable change in pigmentation 
is a decided increase in amount and density in certain well defined 
areas and tracts. The denser pigmentation is especially pronounced 
over the dorsal surface of the head extending posteriorly to the end 
of the medulla. In the median line, however, there is still a narrow 
pigment-free band which extends from the tip of the snout to the 
level of the eye. On the sides of the head the pigment extends 
ventrally to the level of the eyes. The posterior margin of the retina 
is more deeply pigmented than the anterior. The chromatophores are 
no longer found overlying the lens as in the earlier stages. Between 
the posterior margin of the eye and the base of the anterior gill there 
is a broad irregular band which is comparatively free from pigment. 
There are a few chromatophores in the anterior portion of the superior 
maxilla, but none in the inferior. In the trunk there are some notable 
changes in the distribution of the pigment. The mid-longitudinal line 
of the lateral bands now coincides with the large lateral blood vessels 
midway between the level of these vessels. In the mid-dorsal region 
the lateral pigmented bands become less and less dense with the patches 
of chromatophores so irregularly scattered that the band breaks up in 
such a way that it leaves a series of irregular unpigmented. areas, 
which being confluent give rise to a light band. This light band 
extends along the sides of the trunk from the locality of the ear to 
the level of the hind limbs. On either side of the tail the chromato- 
phores form a dark band along its middle portion. The upper portion 
of this surface contains scattered chromatophores while the lower part 
is comparatively free from them. 
In the decapitated larvae of this stage the pigmented areas and 
