THE HEAD AND MOUTH ARMATURE. 41 



its cuticular lining without morphological significance. In my 

 former work* I drew attention to the marked resemblance of 

 these hooks to certain hook-like sclerites in front of the suctorial 

 disc of the proboscis of the imago ; I did not then know how 

 closely this portion of the proboscis is connected with the great 

 hooks of the larva in its developmental history. 



These have only a secondary connection by articulation 

 with the internal pharyngeal skeleton (Fig. 9, ?) which supports 

 them. They are used as organs of locomotion, and probably 

 assist in the disintegration of the flesh in which the larva 

 burrows. 



Before entering upon any further description of the head of 

 the larva, I shall explain the relation of its parts from a de- 



FIG. 7. A vertical longitudinal median section through the anterior portion of a 

 newly-hatched larva seen with inch objective. The external portions of the head 

 are added to the actual section in, invagination of the forehead ; h, lateral 

 (great) hooks ; m, median tooth (labrui) ; /if, stomal disc ; sd, salivary duct ; 

 a, oesophagus ; ad, antennal disc ; od, optic disc ; eg, cephalic ganglia. 



velopmental point of view. The retrogressive character of the 

 final stages of development in the egg has already been alluded 

 to (p. 2). A median section of the newly-hatched larva is 

 given in Fig. 7. A strong median tooth m, is seen deeply 

 imbedded between the maxillae. This tooth is described by 

 Weismann as the most important part of the mouth armature ; 

 it is not present after the first moult and he regarded it as 

 consisting of the united mandibles of the embryo. 



* 'Anatomy and Physiology of the Blo\v-fly.' London, 1870. 



