376 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



The mesodermal tube continues to elongate, its caudal end being 

 drawn more and more into the interior, thus becoming more and more 

 angulated until at the time when the tube is at its maximum length the 

 two limbs of the tube lie parallel with each other. 



Before the union of the mesenteron ribbons on the ventral side, clefts 

 form laterally in the mesoderm, in which, at an earlier period, the lumen 

 had been obliterated. This is the first indication of the definitive haemo- 



stom 



A B 



Fig. 331. — Calliphora erythrocephala. A, sagittal section of anterior end. B, sagittal 

 section of posterior end. {am) Amnion, {am. cav) Amniotic cavity, {ect) Ectoderm. 

 {ent) Entoderm, {mes) Mesoderm, {proct) Proctodaeum. {stom) Stomodaeum. 



coele (body cavity) and of the separation of the mesoderm into the 

 splanchnic and somatic layer. Somewhat later the somatic layer differ- 

 entiates into numerous somatic muscles. The differentiation of the 

 muscles of the mid-gut into transverse and longitudinal fibers occurs in a 

 very late stage of the embryo or possibly even during postembryonic 

 development in the Muscoidea, as is the case also in some other insects. 

 Before the time when head and tail ends lie closest together, the 

 proctodaeal invagination appears at right angles to the amniotic cavity 

 and parallel to the longitudinal axis of the egg. Some of the early 



