Condition of Embryo at end of Second Day 171 



more uncertain. Authors liave recognized three or even 

 four pairs of successive ganglia, which are taken to be 

 the primitive elements of the brain. From the last 

 brain- segment the oesophageal connectives are given off. 

 From the second segment the antennae are innervated. 

 The first segment constitutes the chief mass of the brain, 

 including the optic ganglion \ 



n7x ■•' 



J 





iir 



<n 



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Fig. 125. — Living embryo within the egg, after shortening, 

 in side and front (ventral) view, h-, labrum. lb, labium. 

 at, antenna, md, mandible, mx, maxilla. /, prothoracic foot. 

 Three thoracic and nine abdominal segments are seen in the 

 side view. 



According to AVheeler (1893) the peripheral nerves 

 probably arise as outgrowths of the ganglia, while the 

 stomato-gastric ganglia are developed from the ectoderm 

 of the dorsal surface of the oesophagus. 



At the end of the second day - the body is segmented, Condition 



of embryo 

 ' Viallanes, 1890 ; Wheeler, 1893. at end of 



2 The indications of date here and elsewhere are only approximate. On second day. 

 account of the very different rate of development at different seasons, and 

 of the difficulty in procuring egg-chains immediately after they are laid, 

 it is hard to make tolerably sure of even the order of events. 



