190 GENERAL ZOOLOGY 



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 

 (Fig. 96, 3). 



In the squid's most rapid locomotion the mantle-fins are 

 folded toward the body. In slower movements a wave-like 

 flapping of the fins supplements the jets from the siphon. 

 So skillfully manipulated are the mantle-fins, and the mantle- 

 point itself, in turning to one side or the other, and in going 

 up or down, that one marvels at the wonderful adaptations 

 of an animal that has its "steering-gear" in front, instead of 

 behind, its principal " engine." 



While at rest on the bottom of an aquarium the squid ex- 

 tends its two long arms to the bottom, bent akimbo, appar- 

 ently to keep the siphon and the two lateral mantle-openings 

 away from the sand. The mantle forms the third point of 

 support in the resting attitude. Water may then be drawn 

 into the mantle-cavity, and expelled again, in the normal 

 process of respiration. 



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 seem- 

 ingly 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 disap- 

 pearance of the animals. In times of danger the ability to 

 change color to resemble the environment must be of consid- 

 erable value to them in escaping the notice of enemies, as 

 well as useful in coming unseen into a school of small fish. 



