15 



rhromatophore. Hence Chun in Bolitaena derives the 

 vesicle and the contractile apparatus wholly from one 

 ectodermal cell. He has also traced the nerve supply of 

 the chromatophores. For instance, the pallial nerve has 

 several purely chromato-motor si rands which run 

 outwards to the external epithelium of the mantle, and 

 there divide up ultimately into fine terminal nerves, one 

 of which supplies each radial muscular strand, entering 

 it at the narrow distal end. These nerves control the 

 movements of the chromatophores, and therefore if the 

 pallial nerve be severed the movements of the chromato- 

 phores on the corresponding side of the mantle cease. 

 This method of origin, which Chun has described, may be 

 peculiar to the chromatophores of Bolitaena, and is 

 difficult to reconcile with the account given by Eabl and 

 others. 



In Eledone the pigment granules arc very minute 

 and of a reddish-buff colour. As in all Cephalopods, the 

 motion of the chromatophores continues some time after 

 death. 



Iridocysts. — These are light-reflecting cells embedded 

 in the dermis below the chromatophore layer. They are 

 uninucleate flattened cells, each of which contains two 

 rows of thin fibrillar laminae arranged parallel to one 

 another and reflecting the light, and so giving rise to the 

 peculiar metallic iridescence noticed in the integument. 



II. External Ob#anisation. 



The body may l>e divided into two regions— an 

 anterior cephalopedal mass, and a posterior mass, or 

 r/sr/ nil dome, covered by the mantle. 



As in other Octopoda these two regions are united 

 dorsally by a thin superficial sheet of muscles. 

 Externallv the two regions of the body cannot be 



