34 



between the cartilages above the radula and i-adular )-etractors forms with the 

 lower muscle an obliquely conical tube which contains the radular sac and over 

 whose apex the radular membrane is reflected. 



The radular retractors arise from the dorsal end of the radular cartilages 

 and extending forward parallel to the radula are inserted near the ventral ends 

 of the cartilages upon the subradular membrane. 



The protractors of the radula arise from the lower edge of the upper jaw 

 and passing forward and inward are inserted upon the reflected distal end of the 

 subradular membrane. A small portion of the protractor is inserted upon the 

 toothless portion of the same membrane which , it will l:»e remembered , covers 

 the sides and top of the odontophore. The alternate contraction of the retractors 

 and protractors draws the radula back and forth over the ventral end of the 

 radular cartilages. The teeth act only during retraction hence the retractors are 

 much more powerful than the protractors. 



The mouth , the oesophagus , the radular sac . the median and the paired 

 salivary glands and probably the stomach also arise from the stomadaeum. 



The salivary glands are relatively simple compound-tubular glands. The luraina 

 are large and are surrounded by palisadal cells whose large nuclei are situated 

 next the supporting membrane and whose distal halves are filled bj' large secre- 

 tion vacuoles. The secretion in the lumina is usually precipitated by fixatives. An 

 incomplete series of tests showed that aqueous and glycerine extracts of the median 

 gland are not oleolytic or amjdolytic , and that they are probably proteolytic. 

 Falloise finds this to be the case. The glands also secrete mucin. 



Henze confirms the observations of Lo Bianco, Krause, and Livon & Briot, 

 that the secretion of the posterior salivary glands of various cephalopods injected 

 into the circulation of crustaceans, even in small quantities, is quickly fatal. 

 Henze finds that the poison is an organic base (alkaloid) similar to the poison 

 of bees and of the skin of salamanders. The gland contains also two nitrogenous 

 substances ; one of these, taurin. is vei-y abundant in the muscles of cephalopods, 

 and since von Furth has found very little nitrogen in the secretion of the 

 nephridium , Henze suggests that the gland is , at least in part , excretory. 



The paired or buccal salivary glands are partially imbedded in the muscles 

 upon the dorsal surface of the pharynx Ijetween the radula and the oesophagus. 

 The duct of each gland passes through the palatine lobe and opens into the 

 mouth on the inner side of the lobe near its ventral end. The median salivary 

 gland is a small oval body imbedded in the ventral end of the liver. It lies in 

 a small venous sinus situated beneath the oesophagus and between the diverging 

 visceral and jiallial nerves. Its duct accompanies the oesophagus through the 



