ANATOMY AND HISTOLOGY OF ZIMAX AGRESTIS, 155 
investigations of Troschel (33) and of Geddes (unpublished 
at that time), who ascribed the chief part of the movement 
of the radula to the extrinsic muscles. In the year 1879 
Geddes published his paper on the Mechanism of the 
Odontophore, and stated that in Patella the sliding of the 
radula over the cartilage is only of secondary importance ; 
that the sliding is impossible in Loligo and most impro- 
bable in Buccitnwm. In fig. 1 and fig. 2, Pl. XI., I give 
longitudinal and transverse sections through the head of 
Limaz in the region of the cartilage, and although the 
longitudinal section does not pass right through the median 
line of the head and passes only through the lateral part of 
the diverticulum, it is, however, distinctly seen, that the 
muscles which go from the cartilage to the subradular 
membrane are far less numerous than the muscles which 
connect the two lateral and the anterior and posterior 
surfaces of the cartilage with the body wall. Consequently 
IT have no doubt that the chief part of the movement of 
the radula is due to the extrinsic muscles, although not 
exclusively, as stated by Cuvier. It is scarcely necessary 
to point out that Cuvier, although he is right in general, 
is wrong in regard to one point, namely the functions of 
radula and upper jaw respectively. At present I think 
nobody doubts that the upper jaw has merely the function 
of seizing, and the radula the function of grinding the food. 
The epithelium on the roof of the mouth is provided 
with an extremely strong cuticle, ending anteriorly in the 
crescent-like jaw. In longitudinal section this jaw has the 
form of a tooth (fig. 1, Pl. XI.). The epithelium rests upon 
a layer of beautifully arranged muscle-fibres, which in the 
figure are shown to run in longitudinal, transverse and 
dorso-ventral directions, and this network of muscles 
would seem to enable the upper jaw to move freely in 
various directions, 
