IMAGINAL BUDS OF THE APPENDAGES 665 



segments. These abdominal agglomerations of cells do not give 

 rise to true' buds, but serve simply to reconstitute the hypodermis 

 of the abdominal segments at the time of metamorphosis. 



Ocular or oculo-cephalic buds. The eye of insects, as is well known, 

 is a modification of a portion of the integument, the visual cells 

 being directly derived from the hypodermis, the cornea being a 

 cuticular product of this last, like chitinous formations in general. 



The ocular buds appear towards the end of larval life as a simple 

 mass of hypodermic cells, and form a compact layer on the dorso- 

 lateral face of the prothoracic segment, and clothe the cephalic 

 ganglion or brain like a skull-cap. The central portion only is 

 destined to form the eye, while the peripheral pad, continuing to 

 thicken, gives rise to a voluminous and rounded mass, which meets 

 on the median line that of the opposite side, and forms the integu- 

 ment of all the posterior part of the head. 



Bugnion also observed on the median line a group of small hypo- 

 dermic cells which he regarded as the rudiment of the anterior 

 ocellus, but he did not detect those of the posterior ocelli. 



The antennal buds. These appear at an early date under the 

 cuticle of the head, as two distinct rounded cellular masses, with a 

 central cavity, but no annular zone (Fig. 619, /). Each one grows 

 longer in a transverse sense, and its summit, extended from the outer 

 side, curves downward. It now forms a hollow tube folded at the 

 end, and terminated by a disk whose centre is perforated (Fig. 619, /). 

 Afterwards, when the larva is ready to transform, it grows longer, 

 becomes folded on itself in its cavity, and, passing beyond on each 

 side the limits of the larval head, encroaches on the prothoracic 

 segment. 



The buds of the buccal appendages. Towards the end of the larval 

 period, the buds of the mouth-parts appear as small digitiform pro- 

 jections, situated on each side and below the mouth. Formed of 

 small epithelial cells pressed against each other, they are all directed 

 anteriorly, and possess no furrow or pad. 



The 2d maxillae (labium) is formed of two separate parts. The 

 imaginal buds of the lower lip appear on each side of the median 

 line, with a fissure indicating the differentiation of the palpus. On 

 each side are to be seen the 1st maxillary buds, bearing each a rudi- 

 mentary palpus, and, farther in front, the buds of the mandibles. 



The buds of the ovipositor. The six, stylets of the ovipositor 

 arise from six small imaginal buds which become visible in the 

 second half of the larval period, on each side of the median line, 

 on the lower face of the three last segments (Fig. 620, g 1 , g 2 , g 3 ). 



