ANUEIDA. 365 



and consequently the different regions do not exhibit the 

 complex differentiation into the various sclerites which is 

 seen among the Pterygota. 



The head (fig. 4) is relatively large in size and has 

 its long axis disposed in the same plane as the rest of the 

 body. In form it is somewhat triangular, and it is con- 

 siderably flattened, as if it had been compressed in the 

 dorso-ventral direction. In the mid-dorsal region of the 

 head there is situated a very prominent elevation, shaped 

 rather like an inverted isosceles triangle having each of its 

 angles truncated. From the antero-lateral corners of this 

 protuberance arise the antennae, and on either side of it 

 is a well-marked oval elevation, bearing on its surface a 

 group of glistening black dots. These dots are the eyes of 

 the animal (figs. I and 5) ; they are five in number on each 

 side. A curious circular sense organ, known as the post- 

 antenual organ (p.a.o. in figs 4 and 5) lies on each side 

 just in front of the protuberance just mentioned. The 

 labrum and clypeus (fig. 13) jut forwards in front of the 

 head somewhat in the form of a beak ; they form the roof 

 of the pharynx and somewhat overhang the mouth. The 

 antennas are relatively short, being scarcely as long as the 

 head ; they each consist of four joints, the second being 

 the largest. The articulation between the third and fourth 

 joints is but imperfectly developed, and is only visible on 

 the ventral aspect (fig. 3). The extremity of each 

 antenna is abundantly clothed with hairs, and situated 

 among the latter is a minute trilobed sense-organ (fig. 7) ; 

 a short distance below this structure are several patches of 

 modified cuticle (.s-'.r/.j which may perhaps also be of a 

 sensory nature. The mouth is slightly ventral in position ; 

 it is bounded dorsally by the labrum, ventrally by the 

 labium, and its sides are formed by the oral folds which 

 are prolongations of the sides of the head. The ventral 



