XI 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 vi& 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- 



