14 



epidermis. When the chromatopliores arc thus expanded, 

 the colour of the animal is very deep — this occurs when 

 Eledone is excited in some way. When the radial 

 muscles relax, the chromatophore contracts and the 

 animal becomes pale, as when frightened. In the 

 normally quiet state the chromatophore is in a state of 

 tension, and is shaped like a biconvex disc (II, Chr.). In 

 this stage it is in a semi-expanded condition, the 

 contractile tendency of the two elements being equally 

 balanced. However, the cell is constantly varying 

 slightly in shape, as one or the other of the forces gets 

 the upper hand; and so the chromatophore exhibits 

 incessant slight tremulous movements. Hence when 

 watching Eledone in an aquarium, one is struck by the 

 constantly varying colour of the skin. 



Harting, Blanchard and Girod agree that the vesicle 

 is of ectodermal, and the girdle of mesodermal origin, but 

 they consider that all motion on the part of the 

 chromatophore is due to the amoeboid movements of the 

 vesicle itself, while the radial fibres are connective tissue 

 only. 



Again Chun, who worked on the chromatopliores of 

 Bolitaena, a deep sea form, disagrees with both these 

 views. In Bolitaena the chromatophore arises as a single 

 ectodermal cell which sinks down into the dermis. The 

 nucleus now divides repeatedly, while the cell throws out 

 about 18 pseudopodial processes, in the equatorial plane 

 parallel to the epidermis. At the base of each process is 

 found a corresponding nucleus, which has originated as 

 above. Later it is found that this girdle of processes has 

 become differentiated into a ring of triangular muscular 

 strands, whose contraction serves to expand the 

 chromatophore. A second muscular region becomes 

 differentiated round the periphery of the cell, and this 

 opposes the radial tracks, tending to contract the 



