204 
HISTOLOGY OF ANIMALS. 
fig. 151 . 
are present, but the granules, if not absent, are so few in 
number as to occasion little or no shade of colour. The 
skin of a Lamprey , Fig. 151, exhibits a number of 
large cells of stellate figure, some- 
what like the lacunae of bone. 
The red spots on the skin of 
the Plaice are produced by the 
presence of minute irregular cells 
occurring in great abundance 
between others of large size, 
which are of a black colour, and 
Pigment cells of the skin of stellate figure. Pigment-cells are 
a Lamprey. very frequently found in the 
peritoneum of fishes and reptiles. 
In the skin of a Newt {Triton palmatus), the pigment 
is very abundant, giving a marbled appearance to the 
animal ; the cells are of a stellate figure, and are 
chiefly arranged in circles, the central part of the 
circle being a follicle, which, in some cases, contains 
granular matter. Numerous pigment-cells are present 
in the skin of the web of the frog’s foot ; these always 
excite attention when the circulation in the capillaries 
is seen for the first time. In some of the Reptiles 
there are pigment- cells containing a white material; in 
the iris of a Tiger-boa ( Python tigris ), a collection of 
white pigment-cells exists, in which the branches of the 
cells are of great length, and when these are viewed 
by transmitted light they appear perfectly black. I am 
still uncertain whether the branches of these cells ever 
