334 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



For convenience in description we shall in the present 

 paper speak of the end of the body, where the head is 

 placed, as anterior, and the opposite pointed end as pos- 

 terior; the surface to which the fins are attached we shall 

 call dorsal, and the opposite surface ventral. The student 

 must not infer, however, that these terms are of morpho- 

 logical value, or that the regions which they designate in 

 the Squid are the same as the regions designated by sim- 

 ilar terms in other Molluscs. 



2. Place the animal with its dorsal surface uppermost, 

 and notice : — 



a. The long cylindrical body, ending posteriorly in the 

 pointed, arrowhead-shaped fin. 



h. The small dark-brown pigment spots, or chromato- 

 phores, Avhich cover the surface of the body and head. 

 Examine the chromatophores upon various parts of the 

 body with a lens. In an alcoholic specimen most of them 

 are flat, brown, oval, plate-like bodies, but some may be 

 found in which the outline is irregular, and with radiating 

 processes running out into the surrounding tissues. In a 

 living animal the chromatophores are brightly colored, 

 and are constantly undergoing changes of shape and size, 

 expanding until the edges of adjacent ones almost come 

 into contact, and then contracting to almost invisible spots. 

 Owing to these changes, blushes of color are continually 

 flashing over the surface of the body, and then suddenly 

 disappearing. 



The structure and changes of the chromatophore can be 

 best studied in the small transparent embryos, which are 

 frequently to be found at the surface of the ocean during 

 the summer months. 



c. Anteriorly the body proper ends in a free edge or 

 collar, the margin of the mantle, which is separated from 

 the head by an interspace, the mantle chamber. 



