CHAPTER XVII 

 NEUROPTERA AND COLEOPTERA 



NEUROPTERA 



The Alder Fly (Sialis Maria L.) 



The eggs of this insect are usually found attached to the leaves of 

 water plants. The developing egg, as described by Strindberg (1915), 

 undergoes cleavage and forms a pri- 

 mary epithelium (blastoderm) in a 

 normal way, yolk cells remaining 

 behind in the outward migration of 

 the cleavage nuclei. The germ band 

 forms ventrally on the posterior two- 

 thirds of the egg. The nonembryonic 

 part of the blastoderm, which will 

 form the serosa, is composed of two 

 parts: the anterior part, covering the 

 anterior third of the egg made up of 

 columnar cells; and the posterodorsal 

 part, made up of thin fiat cells. A 

 deep posterior and a shallow anterior 

 amniotic fold develop. As they be- 

 come progressively longer, the flat 

 dorsal serosa cells become greater in 

 extent at the expense of the deep 

 anterior serosa cells. Soon amnion 

 and serosa are completed. Mean- 

 while the embryo elongates ; the inner 

 layer forms through immigration or 

 through a feebly indicated invagina- 

 tion along the median longitudinal 

 ventral hue proceeding from behind 

 forward. As interpreted by Strind- 

 berg, the anterior end of the inner 

 layer forms chiefly the anterior ento- 

 derm rudiment ; the middle part, the mesoderm; and the posterior end, the 

 posterior entoderm rudiment. The mesoderm is segmentally arranged, 

 the lateral edges of each somite becoming reflexed to form the coelomic 



285 



ser 



mgc 



mge 



proct- 



Fig. 215. — Sialis. Longitudinal sec- 

 tion, {am) Amnion, (br) Brain. (Jg) 

 Frontal ganglion, (mge) Mid-gut epi- 

 thelium, (proct) Proctodaeum. (ser) 

 Serosa. {stom) Stomodaeum. (yc) 

 Yolk cells. 



