140 Descriptive Zoology. 



similar in shape to a feather. This is imbedded in the dor- 

 sal part of the mantle, extending nearly the whole length of 

 the back. It is wholly inclosed in a capsule in the thick- 

 ness of the mantle wall. 



The Siphon or Funnel. Projecting from the mantle 

 cavity under the head is a funnel whose narrow end opens 

 forward and whose wide end points back into the mantle 

 cavity. 



How the Squid Swims. Water is taken into the mantle 

 cavity through the open space around the neck. Then 

 the edge of the mantle is contracted and is fastened to the 

 neck and sides of the base of the funnel by a set of car- 

 tilages that have a sort of " hook and eye " arrangement. 

 Then by the contraction of the mantle the water is forced 

 out through the siphon, and by reaction the squid is rapidly 

 driven backward through the water. So swift is its move- 

 ment that it has received the popular name of " arrow fish." 

 Squids sometimes dart clear out of the water, and, when 

 kept in aquariums, thus jump over the sides. Their mo- 

 tion is amazing, not only on account of its swiftness, but 

 because there is no manifest cause of the motion. They 

 propel themselves by the outgush of water, which is in- 

 visible, and the change in size from the contraction of the 

 mantle is so slight as to be unnoticed. To the uninstructed 

 it is as inexplicable as the motion of a trolley car is to 

 a savage. When the squid wishes to move slightly, it 

 does so by gently flapping the tail fins. 



The Ink Bag. The squid has an ink bag, which lies 

 near the rectum, and which opens near the anal opening, 

 near the inner end of the funnel. When in flight from a 

 pursuing fish, a discharge of ink is sent out in the strong 

 gush of water through the siphon. This makes a dark 

 cloud in the water, under cover of which the chances of 



