VERTEBRATES FROM A CRUSTACEAN-LIKE ANCESTOR. 415 



which contain thenij and their absorption into the cells of 

 the connective tissue. Ultimately the formation of regularly 

 arranged pigmented connective tissue is complete, and in the 

 adult animal the circulation has become so modified that such 

 marked stagnation no longer occurs. 



In the whole life of the animal, as far as I have had an oppor 

 tunity of judging at present, the time when most pigment is 

 accumulated in the walls of the blood spaces of the branchial 

 and other regions is just before the time of transformation. 

 In the embryo, as shown by Shipley's specimens, very little 

 pigment is to be found. In the adult, again, the pigment in 

 the internal regions is much less apparent than in the full- 

 grown Ammocoetes; and indeed it seems to me probable that 

 not only are the pigment-granules arranged in an orderly manner 

 in the connective-tissue cells after the metamorphosis of the 

 animal, but also that a considerable proportion is got rid of, 

 perhaps after the fashion described by Eisig (17), by excretion 

 into the skin. 



This process of the formation of pigment, as I have 

 imagined it to be taking place in the Ammocoetes, is in strict 

 harmony with what is known to occur in the liver of the 

 frog, and in pathological cases of cirrhosis of liver accompanied 

 by pigmentation. Thus Hunter describes the occurrence of 

 cirrhosis in the liver of a rabbit as a result of the presence of 

 pigment. In one experiment he found a form of perilobular 

 cirrhosis, some of the lobules being entirely replaced by small- 

 celled connective tissue. In each case the seat of formation 

 of this tissue corresponded with the presence of larger or 

 smaller heaps of pigment. In a case of cirrhosis in man he 

 found similar appearances, and also in the liver of pigeons. 

 The large size of the red corpuscles in birds renders their 

 arrest within the capillaries of the liver very easy after they 

 have undergone passive destruction, and become converted 

 into rigid pigment masses. Wherever they become arrested 

 a proliferation of the cells of the capillary walls takes place, 

 and the small clumps soon become surrounded by a small-celled 

 growth of connective-tissue cells. He concludes that in all 



