214 THE MORPHOLOGY OF THE COMMON CRAYFISH. 
which the cavity of the fore-gut communicates with that 
of the mid-gut (fig. 57, E). Thus a gullet and stomach, 
or rather the parts which will eventually give rise to all 
these, are constituted. And it is important to remark 
that, in comparison with the mid-gut, they are, at first, 
very small, 
In the same way, the epiblast covering the sternal face 
of the abdominal papilla undergoes invagination and is 
converted into a narrow tube which is the origin of the 
whole hind-gut (fig. 57, C, and fig. 58, E, hg). This, like 
the fore-gut, is at first blind; but the shut front end soon 
applying itself to the hinder wall of the archenteric sac, 
the two coalesce and open into one another (fig. 57, E). 
Thus the complete alimentary canal, consisting of a very 
narrow, tubular, fore- and hind-gut, derived from the 
epiblast, and a wider and more sac-like mid-gut, formed 
of the whole hypoblast, is constituted. 
The procephalic lobes become more convex; while, 
behind them, the surface of the epiblast rises into six 
elevations disposed in pairs, one on each side of the 
median groove. The hindermost of these, which lie at 
the sides of the mouth, are the rudiments of the 
mandibles (fig. 58, EK and F,4); the other two become 
the antenne (8) and the antennules (2), while, at a later 
period, processes of the procephalic lobes give rise to the 
eyestalks. 
A short distance behind the abdomen, the epiblast 
rises into a transverse ridge, which is concave forwards, 
