The anatomy of Lottia gigantea Gray. 37 



be seen from several points of view. In each succeeding figure taken 

 in the order of 3, 10, 9, 4, 5, 16 and 13, a few muscles have been 

 removed so as to uncover deeper-lying ones. In this manner it is 

 believed the relationships of the several groups can be clearly seen. 

 Bilateral symmetry is observed in all the muscles, or groups of muscles. 

 The retractors of the buccal mass (5) are attached to the posterior 

 processes of the cartilage and originate ;on the floor of the head 

 cavity between, and just in front of the pedal ganglia. Auxiliary ob- 

 lique muscles {13) are found in connection, which act as depressors, 

 and permit of a lateral movement of the mass. The protractors 

 are much heavier than the retractors and there are two sets of them 

 on each side, namely the lateral (7) and right and left inferior pro- 

 tractors (8). The latter originate just behind the mouth on the floor 

 of the head cavity and are inserted near the retractors on the posterior 

 processes of the cartilage. It is probable that muscles 10 and 12, 

 especially 12 which passes from the lateral processes or knobs 

 of the cartilage to the dorsal wall of the head cavity , may 

 act in manipulating the buccal mass as a whole. Two very 

 well developed sets of muscles work the radula. The major re- 

 tractor of the radula (i) is very conspicuous, being disposed in 

 cord-like bundles, which, originating on the latero- ventral surface of 

 the cartilage, pass up over the top and are inserted along the edge 

 of a horny wing-like expansion of the forward end of the radula 

 (Figs. 4 and 16 1). Under this, next to the cartilage, is a tendinous 

 sheet, the minor retractor of the radula (Fig. 16 5), which originates 

 on the posterior process, and ventral side of the cartilage, and is in- 

 serted along the under side of the wing-like expansion of the radula 

 (stippled 2'). This muscle must have a splendid purchase on the 

 whole expanded portion of the radula. The protractor of the 

 radula (9), in texture resembles the major protractor, and originates 

 on the posterior knob or process of the cartilage, passes along its 

 ventral surface and is inserted on the horny wing of the radula, 

 below the major retractor. Fig. 4 shows the relation between these 

 two. Muscles 10 and 11 (l^'ig. 10) also probably act as protractors 

 of the radula tube. Muscle â seems to act as a retractor of the 

 dorsal lip of the radula tube. Contractions of the set marked 5 

 (Figs. 9 and 10) would widen the oral cavity. They are inserted 

 along the heavy lateral folds of the buccal cavity. The retractors of 

 the palps (6') originate on the posterior knobs of the cartilage and 

 pass directly forward to be inserted all along the interior of the 



