216 GENERAL ZOOLOGY 



The conical portion of the body is the mantle, highly 

 modified by the existence of strong, muscular bands. Part 

 of the space within the muscular mantle is occupied by the 

 internal organs inclosed in a body cavity. The remainder 

 of the space, the mantle cavity itself, connects with the 

 outside by a narrow opening, at either side of the neck, 

 and also by the siphon. A pair of feather-shaped gills, one 

 attached to either side of the body, lies in the mantle cavity. 

 Imbedded in the tissue of the mantle, on the side opposite 

 the surface shown in the figure, there is a long, pen-shaped 

 structure composed of chitinous material. This represents 

 the remains of the shell. The sexes are separate. 



In locomotion the squid contracts and relaxes the circular 

 muscles of the mantle, alternately decreasing and increas- 

 ing the volume of the mantle cavity. During relaxation, 

 water enters the mantle cavity at the sides by the neck, a 

 valve in the siphon being closed ; in contraction the valves 

 at the side openings are closed and the water is discharged 

 through the siphon. The siphon may be directed forward 

 or backward at will. If it is bent in the direction of the 

 arms, as it commonly is, the squid during strong contraction 

 of the mantle darts backward "with the speed of an arrow," 

 balanced and steered by the aid of the double mantle fin. 



No more beautiful example of rapid color change can be 

 witnessed than the one going on constantly in the skin of 

 captive squids. From bluish white the color may change on 

 the instant to mottled red or brown. The change may be 

 sudden and complete, or the colors may fluctuate repeatedly 

 from one shade to another and shimmer over the surface 

 seemingly as rapidly as the controlling nerves can act. 

 Observers who have been fortunate enough to come upon a 

 'school" of squids in a harbor have been puzzled by the 

 sudden disappearance of the animals. In times of danger 

 the ability to change color to resemble the environment 



