114 



THE APOD1D/E 



PART I 



might become differentiated into a masticatory 

 stomach, such as we find in the higher Crustacea. 

 No such differentiation is, however, visible in Apus. 

 In Limulus we shall find the chitinous ridges used 

 for masticatory purposes in what is called the pro- 

 ventriculus, which is homologous with the masticatory 

 stomach of the higher Crustacea. 



The oesophagus projects somewhat into the mid- 



FIG. 29. Diagram of the branched diverticula of the anterior end of the mid-gut (;), 

 on the left without the glandular (hepatic) branched cocca, on the right a few of 

 the latter are drawn, a?, entrance to the oesophagus, on each side of which are 

 seen two long glands opening together in the middle line, assumed to be the 

 acicular glands of the vanished parapodia of the first antennal segment. 



gut, which is a large sac with lateral diverticula five 

 or six on each side ; these unite, in Apus, to enter 

 the mid-gut together (Fig. 29). These diverticula fill 

 up the large flat head widened by the ridge run- 

 ning round the frontal region, as already described. 

 Diverticula of the mid-gut are common among 

 Annelids, and serve to increase the digesting surface. 

 The diverticula of Apus are especially interesting 



