56 THE CLASS OF INSECTS. 



ceals the base of the antennje. It is probable that more 

 careful observation would have shown the end of the abdomen 

 folded back upon the dorsal region, as usual at this period in 

 the embryos of those insects whose embryology has been 

 studied. 



The antennffi, mandibles, and maxilla} form a group by them- 

 selves, while the second maxillae (or labium) are very much 

 larger and turned backwards, being temporarily grouped with 

 the legs. 



There are traces only of the tAvo basal sterna of the abdo 

 men. This indicates that the basal abdominal segments grow 

 in succession from the base of the abdomen, the middle ones 

 appearing last. The post-abdomen (Fig. 59 a) has probably 

 been developed synchronous with the procephalic lobes, as it is 

 in all insect and crustacean embryos 3'et observed. As stated 

 by Zaddach, these two lobes in their development are exact 

 equivalents; antero- posterior symmetry is very clearly de- 

 marked, the two ends of the body at first looking alike. But 

 in this stage, after the two ends of the body have been evolved 

 from the primitive cell-layer, development in the post-abdomi- 

 nal region is retarded, that of the head progressing witli mucli 

 greater rapidity. 



In the next stage (not figured) the yolk is completely walled 

 in, though no traces of segments appear on the back or side of 

 the embryo. The revolution of tlie embr^^o has taken place ; 

 the post-abdomen being curved beneath the body, and the back 

 presenting outwards. 



The rudiments of the ej^es appeal* as a darker, rounded mass 

 of cells indistinctly seen through the yolk-granules, and situ- 

 ated at the base of the antennaj. They consist of a few epithe- 

 lial cells of irregular form, the central one being the largest. 



The second maxillae are a little over twice the length of the 

 3rst maxilltB and are grouped with the legs, being curved bacli- 

 A'ards. They are, however, now one-third shorter than the an- 

 terior legs. The second maxillary sternum is still visible. 



The tip of the abdomen (or post-abdomen) consists of four 

 segments, the terminal one being much the larger, and ob- 

 scurely divided into two obtuse lobes. 



The abdominal sternites are now well marked, and the nei*- 



