DEVELOPMENT 155 
Entoderm.—At its anterior and posterior ends, the inner 
fayer just referred to gives rise to a mass of cells which are 
Hie. 201, 
Transverse section of abdomen of Clytra embryo at an advanced stage of develop- 
ment. a, appendage; e, epithelium of mid intestine; g, ganglion; m, Malpighian tube; 
mi, muscular layer of mid intestine; ms, muscle elements; my, mesenchyme (source 
of fat-body); s, sexual organ; t, tracheal invagination.—After LécaILLon. 
destined to form the mesenteron, from which the mid intestine 
develops. One mass 1s adjacent to the blind end of the stomo- 
dzeal invagination and the other to that of 
the proctodeal in-folding. The two 
masses become U-shaped (Fig. 202), and 
the lateral arms of the two elongate and 
join so that the entodermal masses become 
connected by two lateral strands of cells; 
by overgrowth and undergrowth from 
these lateral strands a tube is formed 
which is destined to become the stomach, 
and by the disappearance cf the partitions 
that separate the mesenteron from: the 
stomodzeum at one end and from the proc- 
todeum at the other end, the continuity 
of the alimentary canal is_ established. Ppa 
The fore and the hind gut, then, are  tarsa. e, e, entodermal 
ectodermal in origin, and the mid gut st aaa 
entodermal. 
