i6o Embryonic Development of Chironomns 



seen to be connected by streaks or paths of clear proto- 

 plasm. These nuclei are the first indications of the 

 somatic cells, from which the tissues of the body of 

 the insect will be derived. They 

 multiply with great rapidity, travel 

 towards the surface of the egg, pro- 

 bably accompanied by protoplasm, 

 and arrange themselves side by side 

 in the peripheral protoplasmic layer, 

 which bulges a little outwards over 

 each nucleus, but is otherwise con- 

 tinuous and uniform ; it is sharply 

 separated from the yolk within (fig. 

 119). This layer is the hlastoderm ; 

 it gives rise to the future body, and 

 also to certain temporary structures 

 connected with it. The nucleated 

 blastoderm aj)pears almost suddenly, 

 and being transparent, curved, and 

 refringent, it is a matter of great 

 difficulty to study its formation at 

 all closely. The nuclei are at first 

 few and large, but rapidly increase 

 in number and diminish in size. 

 An inner, clear, protoplasmic blas- 

 tema, deepest at the two poles, forms 

 within the blastoderm ; the invest- 

 ing cells extend into this, and absorb 

 or appropriate it, thereby doubling 



Fio. 119. — I, Longitudinal 

 section of lilastoderm. n, 

 nuclei. ?/, yolk, s.g, sexnal 



germs. '2, Hinder end of the depth 01 the blastoderm ; the 



blastoderm, to illustrate the i • i 1 1 l • i 



re-entry of the sexualgerms. UUClCl at tllC SaUlC tllUC bCCOlUe 

 W, blastoderm, s.gr, sexual 

 germs. (From Eitter, 1890, 

 figs. 9, 10 ) 



same 

 temporarily elongated in a direc- 

 tion perpendicular to the surface 

 of the egg. The formation of a single cellular layer 

 enclosing the yolk has often been cited as an example of 



