GENERAL ANATOMY OF THE SQUID. 337 



which consists of a long, sleuder, cylindrical' shaft, termi- 

 nating in a large rhomboidal expansion, upon which are 

 four rows of cup-shaped suckers or acetabula, while the 

 remaining eight arms have two rows each of acetabula. 



/. Make a sketch of the ventral surface. 



g. Examine the acetabula with a hand lens ; notice : 



(1.) The short peduncle or stem. 



(2.) The enlarged terminal cup, on the outer or flat 

 surface of which notice : 



(a.) The membraneous marginal lip, which encircles the 

 aperture. 



(/;.) Inside this a horny ring, with its outer or exposed 

 edge serrated with fine teeth. 



(c.) Within this a shallow cavity, at the bottom of 

 which is a flat surface, the piston. 



(V.) Cut a longitudinal section of one of the acetabula, 

 and with a hand lens notice that the piston is made up of 

 a mass of muscles, which are attached to the bottom of 

 the cup, and so arranged as to pull back the piston, by 

 which the sucking action of the acetabula is affected. 



II. The Mantle Chamber. 



Xotice that while the anterior edge of the mantle is not 

 attached to the head at any part of its circumference, it is 

 in contact with it at three nearly equidistant points, on 

 the median dorsal line and at the sides. Open the mantle 

 cavity by an incision through the integument, from the 

 anterior margin nearly to the posterior end, and a little to 

 the left of the median line. Place the animal under 

 water, and turn back the halves of the mantle, in order to 

 expose its cavity. Xotice that while the mantle cavity 

 extends upon the sides and ventral surface, nearly to the 

 posterior end of the body, it is quite shallow on the me- 

 dian dorsaj line, and about an inch from its anterior mar- 

 gin the mantle is joined to the neck. 



