59 



part of the egg is left only covered by the ectoderm 

 (fig. 78, mes.). 



The various appendages appear for the most part in a 

 regular succession from before backwards (fig. 71). The 

 antennae are the first pair to develop, and they are followed 

 by the medium unpaired rudiment of the labrum and 

 clypeus. Behind the former there arise in rapid succession 

 the mandibles, the first and second maxillse, the three pairs 

 of thoracic feet, and a pair of appendages to each of the 

 first four abdominal segments. Between the antennae and 

 mandibles there are developed a pair of transient trito- 

 cerebral or intercalary appendages (fig. 7o). They were 

 first discovered in this insect by Wheeler, and both 

 Claypole and Folsom have since confirmed their existence. 

 A little later there arise between the mandibles and first 

 maxillae the rudiments of another pair of mouth-parts 

 iiii.vuJ. in fig. 75). These have been recently discovered by 

 Folsom, and were named by him the super-linguae, but, 

 as already stated (footnote p. 19), the term maxillulae is 

 preferable for them. About this time the rudiments of 

 the stomatodieal and proctodaeal invaginations become 

 visible, and the dorsal organ commences to degenerate. 

 A very marked flexure of the embryo now takes place, and 

 when it is complete the latter becomes more or less folded 

 on itself (fig. 72). The result is that whereas the anterior 

 end of the embryo retains its relations with the pre- 

 cephalic organ, the anal portion becomes retracted away 

 from the latter, and the embryo itself becomes restricted 

 to less than one-half of the whole circumference of the 

 egg, instead of completely encircling it, as happened in 

 the earlier stages. Furthermore, the mouth-parts become 

 crowded together to form a definite head. The last mouth- 

 part to appear is the lingua, which does not become 

 visible until after the flexure of the embrvo has 



