NEUROPTERA AND COLEOPTERA 



303 



coel). At this time the neural groove is deep, and ectodermal cells on each 

 side differentiate to form the neuroblasts. The tracheal system has 

 also started, developing tracheal invaginations {tr) occurring in eight 

 segments of the abdomen. Later on, two pairs of tracheal openings will 



^^'ir 



^m0 "^"'"s 5^ 



Fig. 247. — Brachyrhinus. Cross section through the thorax of 90-hour embryo, (fiod) 

 Coelomic cavity, {neurg) Neural groove, (tr) Tracheal invagination. 



be evident in the thorax. These appear clearly on the eighth day (Fig. 

 248). 



Between the fourth and the eighth days, the embryo grows laterally 

 around the yolk and becomes shorter until the caudal end Kes at the 

 posterior pole of the egg. At first the gnathal and thoracic appendages 

 as well as the antennae are elongate and slender (Fig. 245). Soon they 



Eight-day 



Fig. 249. — Brachyrhinus. 

 Ten-day embryo. 



become reduced to mere lobes, and processes identical with them appear 

 on abdominal segments one to eight (Fig. 248) on the eighth day. Two 

 days later the abdominal lobes disappear (Fig. 249). By the eighth 

 day the gnathal segments have moved cephalad and have begun their 

 fusion with the head lobes. At this time the intersegmental sutures have 



