74 Invertebrate Zoology. 



openings. It lies between and dorsal to the siphonal re- 

 tractors, and is pierced at its anterior end by the oesophagus, 

 which courses along its dorsal surface. 



The oesophagus finally enters the smaller, more muscular, 

 cardiac portion of the stomach. By blowing with a blow- 

 pipe into the cardiac portion, the much larger and thin- 

 walled gastric sac will become inflated. This organ is a 

 "blind-sac" and extends to the posterior end of the mantle 

 cavity. It often contains partially digested food bits of 

 fish, etc. 



Trace the intestine from its origin, near where the oesopha- 

 gus enters the stomach, to the rectum. If the gastric sac is 

 already filled with water, it may be rolled from its original 

 position, clearly showing its relations to the other neighbor- 

 ing organs. 



Make a drawing of the entire digestive system as seen from 

 below, and also as seen from the side, naming all the parts. 



The Muscular System. The Cephalopods are most 

 active Invertebrates and the muscular system is correlatively 

 developed. Muscle tissue largely makes up the outer sub- 

 stance of the animal, though there is a remarkable lack of 

 clearly defined muscle bundles. The retractors of the head 

 and siphon are, however, more definitely isolated. 



Reproductive System of the Male. As the gastric 

 sac is partly removed, note on the posterior dorsal wall of 

 the mantle cavity the large testis." It is firm in texture and 

 somewhat elongate-oval in outline. Leading to the testis 

 from the region of the cardiac stomach is an artery which 

 pierces the delicate capsule in which the organ lies. At 

 the left of the testis, the accessory reproductive organs of the 

 male are to be observed. They form an irregular mass 



