XX 
THE COLOURS OF REPTILES 
239 
row at a later stage fuses with the first of the upper 
row at each side, and the two large spots lying close 
together form the black part of the “ collar ” of the 
adult. The author does not state what becomes 
of the unpaired median red line, it presumably dis¬ 
appears without being replaced by pigment spots, 
but its presence is interesting in view of the fact that 
the lizard has a black line in this region. 
An examination of the red lines, by means of 
sections, shows that they are due to superficial 
blood-vessels connected at regular intervals with the 
deeper vessels of the body. The median red line 
of the three laterals corresponds to a vein called the 
epigastric which receives blood brought back from 
the vessels of the skin, and transmits it via a series 
of transverse vessels to the deeper veins, e.g. the 
cardinal vein. The first appearance of pigment, 
except in the choroid, is in connective tissue cells 
lining the body cavity, and these appear to spread 
round about the epigastric, though this is uncertain. 
At any rate the epigastric vein loses its endothelial 
lining, becomes filled with connective tissue cells, and 
is gradually obliterated, the obliteration being pre¬ 
ceded by a formation of direct connections between 
the vessels of the skin and the transverse vessels, so 
that the epigastric vein is thrown out of the circula¬ 
tion. At this period the pigment spots are developed, 
and they occur in the cutis opposite the points where 
the transverse vessels formerly entered the epigastric. 
A similar relation exists between the other rows of 
spots and blood-vessels. 
Herr Zenneck leaves undecided the question 
whether the pigment originates entirely in the con- 
