178 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



they later unite with the cells of the anterior and posterior mid-gut 

 epithelial ribbons. The middle strand gives rise to the blood cells. As 

 development goes on, stomodaeum and proctodaeum become longer, the 



n 



Fig. 90. — Isotoma. Sagittal section 

 through head. (am. ser) Amnioserosa. 

 {hr) Brain. {Ir) Labrum. {mge) Mid- 

 gut epithelium, {mus) Muscle, (n) 

 Nerve tissue, (stom) Stomodaeum. (yc) 

 Yolk cell. 



mge 



procf — rnus 



Fig. 91. — Isotoma. Sagittal sec- 

 tion of posterior end of body. (am. 

 ser) Amnioserosa. (mge) Mid-gut ep- 

 ithelium, (mus) Muscle, (n) Nerve 

 tissue, iproct) Proctodaeum. 



former somewhat geniculate (Fig. 92), the latter widening at the tip and 

 freed from inner-layer cells. Malpighian tubules do not develop. 



The cells of the anterior and posterior cell masses (mid-gut epithelium 

 rudiments) now enlarge; from each lateral edge a cell strand arises, the 

 two arising from the stomodaeum growing backward, those from the 



Fig. 92. — Isotoma. Sagittal section of anterior end. (hr) Brain, (do) Dorsal organ. (Ir) 

 Labrum. (mus) Muscle, (n. ggl) Nerve ganglion, (stom) Stomodaeum. 



proctodaeum growing forward (Fig. 93) until these strands (ribbons) 

 meet. The widening of the ribbons soon causes them to unite below, thus 

 forming the lower wall of the ventriculus and later, by the increasing 

 width of the ribbons, closes the alimentary canal on the dorsal side also. 



