ORIGIN OF THE INTERNAL ORGANS. 223 
Becoming constricted in the middle, the fore-gut next 
appears to consist of two dilatations of about equal size, 
connected by a narrower passage (fig. 57, E, fg', fg*). 
The front dilatation becomes the cesophagus and the 
cardiac division of the stomach; the hinder one, the 
pyloric division. At the sides of the front end of the 
cardiac division two small pouches are formed shortly 
after birth; in each of these a thick laminated deposit 
of chitin takes place, and constitutes a minute crab’s-eye 
or gastrolith, which has the same structure as in the 
adult, and is largely calcified. This fact is the more 
remarkable as, at this time, the exoskeleton contains very 
little calcareous deposit. In the position of the gastric 
teeth, folds of the cellular wall of corresponding shape 
are formed, and the chitinous cuticle of which the teeth 
are composed is, as it were, modelled upon them. 
The hind-gut occupies the whole length of the abdo- 
men, and its cells early arrange themselves into six 
ridges, and secrete a cuticular layer. 
The mid-gut, or hypoblastic sac, very soon gives off 
numerous small prolongations on each side of its hinder 
extremity, and these are converted into the ceca of the 
liver (fig. 57, EH, mg). The cells of its tergal wall are in 
close contact with the adjacent masses of food-yelk; and 
it is probable that the gradual absorption of the food- 
yelk is chiefly effected by these cells. At birth, however, 
the lateral lobes of the food-yelk are still large, and 
occupy the space left between the stomach and liver 
