THE DEVELOPMENT OF THE NYMPH. 



325 



In the resting larva and pronymph the neuroblast increases 

 rapidly in size, and, as already stated, its position varies at 

 different stages of the development of the cephalo-thoracic discs. 



Fig. 46. — A semi-diagrammatic seciion of one of the hemispheres, the optic cup and 

 optic disc from a pronymph on the third day of the pupa stage : a c, anterior 

 commissure ; a g, antennal ganglion ; d, optic disc ; a; oesophagus ; s, optic 

 stalk ; r f, retinal disc ; r s, retinal stalk, connecting the cup-like disc with the 

 optic ganglion, which is seen surrounding its inner extremity ; O; tiabecula. 



During the evolution of the head discs on the second or third 

 day of the pupa state, the hemispheres, which up to this period 

 remain approximately spherical, become pyriform, and a groove 



