266 COLLEGE ZOOLOGY 



(Fig. 191, 1); these fins may propel the squid slowly forward 

 or backward by their undulatory movements, or may change 

 the direction of the squid's progress by strong upward or 

 downward strokes. 



The shell or pen of Loligo (Fig. 192, Pn) is a feather-shaped 

 plate concealed beneath the skin of the back (anterior 

 surface). 



The true head is the short region between the arms and the 

 mantle collar; it contains two large eyes (E). 



The digestive system includes a pharynx or buccal mass (Fig. 

 192, Ph), oesophagus, salivary glands, stomach (St), c cecum (Ca), 

 intestine, rectum, inksac (IS), liver, and pancreas. There are two 

 powerful chitinous jaws in the pharynx ; they resemble a par- 

 rot's beak inverted, and are moved by strong muscles. A rad- 

 ula is also present. Two salivary glands lie on the dorsal surface 

 of the pharynx, and one is embedded in the ventral end of the 

 liver; they all pour their secretions into the mouth. The oesoph- 

 agus leads from the pharynx through the liver and into the stom- 

 ach. Closely connected with the muscular stomach is the large, 

 thin-walled caecum. Food is probably partially digested in the 

 stomach by fluids brought in from the pancreas and liver; it 

 then passes into the caecum, where digestion is completed and 

 absorption takes place. Bones and other indigestible material 

 are forced from the stomach into the intestine and out through 

 the anus (An). 



The blood of the squid is contained in a double, closed vascular 

 system. Arterial blood is forced by a muscular systemic heart 

 to all parts of the body by three aorta : (1) anterior, (2) posterior, 

 and (3) genital. It passes from arterial capillaries into venous 

 capillaries, and thence into the large veins. From these it enters 

 the right and left branchial hearts, and is then forced into the 

 gills through the branchial arteries. In the gills the blood is 

 aerated, and is finally carried by the branchial veins back to the 

 systemic heart. 



There are two gills in the squid (Fig. 192, Gi). The water 



