43 



(Girod). The duct opens into the anal chamber and its distal end is surrounded 

 by a sphincter. The wall of the ink sac is formed of an outer sheet of connec- 

 tive tissue, a middle sheet of circular and longitudinal muscle fibres, and an 

 inner sheet of pavemental epithelium. The reservoir has an additional layer 

 situated between the epithelium and the muscular layer. This layer is about as 

 thick as the other layers combined and is formed of iridiocysts whose fibres 

 reflect light and give the ink sac its beautiful silvery luster. The jet black ink , 

 as is well known , is discharged into the water and produces a black cloud under 

 cover of which the squid may escape an enemy. Such a provision is very useful 

 to an animal which has neither protective skeleton , efficient defensive organs , 

 nor the power of sustained rapid motion. The ink of Sepia is composed of 

 melanin, which is produced by the action of a ferment, tyrosinase (von Furth) 

 and which is accompanied by laccase (Gessard). 



In conclusion it may be well to describe the very interesting manner in 

 which the squid captures and eats its prey. While stalking the prey, the squid 

 swims lazily forward and backward in a zig-zag line, gradually approaching the 

 animal which is to be captured. This motion is produced by jets of water ejected 

 through the siphon which is turned forward to drive the squid backward, and 

 backward to drive it forward. The fins keep up a slow undulating motion by 

 means of which the back end of the body is guided in the proper direction. At 

 the same time the arms are pressed together to form a lance-shaped fin which 

 is generally bent upward while the siphon is turned forward , and the squid is 

 going backward: and is bent downward while the siphon is directed backward 

 and the squid is moving forward. The squid having come sufficiently near, tul'ns 

 its head toward the prey and by a powerful contraction of the mantle, drives 

 a jet of water backward through the siphon and shoots forward like an arrow. 

 Just as it reaches its prey, the sessfle arms spread outward like the rays of a 

 chrysanthemum and the tentacles are driven forward so that they are pressed 

 against the prey which is quickly drawn back to the mouth and grasped by the 

 sessile arms. Sometimes a fish is wary and repeatedly escapes the attack so 

 that the squid appears to give up the chase. Squid are often kept in the aquaria 

 of the United States Fish Commission at Woods Hole and fed upon mummichogs 

 and other small fish. At one time we noticed among the mummichogs, one that 

 was especially wary and agile so that it successfully avoided the attacks of 

 several squid for some time after the other fish had been captured. One of the 

 squid dropped to the bottom and grasping the gravel with its suckers anchored 

 itself and at the same time adjusted its chromatophores so that it was as 

 inconspicuous as possible. The squid lay thus upon the bottom until the mum- 



