VEETEBRATES FROM A CRUSTAOEAN-LIKE ANCESTOR. 409 



One of the most striking characteristics of this degenerated 

 liver-tissue is the presence of so much pigment in between its 

 cells and lining the surface of the brain. What^ then, is the 

 meaning of this pigment ? 



Sect. 6. — The Formation of Pigment. 



The almost universal source of pigment in the Vertebrate 

 kingdom is the colouring matter of the blood ; we must, there- 

 forCj look especially to the destruction of red blood-corpuscles 

 in order to account for the presence of pigment in the majority 

 of instances. 



Recently a paper has appeared by Hunter (16), who has 

 been occupied for a long time in the investigation of the nature 

 of the destruction of the red blood-corpuscles. He concludes 

 that pigment is formed from the haemoglobin of the blood- 

 corpuscles in two distinct ways, called by him respectively 

 Active and Passive destruction, and defined as follows : 



Active destruction is that form of disintegration of the 

 red blood-corpuscles where the hsemoglobin is liberated and 

 escapes into the plasma -, it is the change in the blood-corpus- 

 cles which is caused by the action of water, various salts, &c. 

 The chief evidences of this active destruction are — (1) the 

 formation of bile-pigments by the liver, to which organ the 

 haemoglobin thus set free is mainly carried ; (2) to a secondary 

 and altogether subsidiary extent in health, the formation of 

 blood-pigment. 



The chief characters of this blood-pigment are the small 

 uniform size and spherical shape of its individual particles. 

 The size of the red corpuscles have no influence on the size of 

 the pigment particles resulting from active destruction. It is 

 the same in mammals as in birds or amphibians. The pig- 

 ment is formed from free haemoglobin. 



Passive destruction of the blood-corpuscles, on the other 

 hand, is a slow and gradual decay of the red blood-corpuscles. 

 The haemoglobin remains in the corpuscle to the last, and 

 becomes gradually converted into a globule of inert blood- 

 pigment. 



