241 



MYRIOPODA. 



The Alimentary Canal. 

 In treating of the formation of the alimentary canal, we must keep 

 the Chilopoda and the Diplopoda quite distinct from each other. 

 The accounts as yet given of the origin of the intestine in the 

 Diplopoda, indeed, are by no means detailed, and do not throw 

 sufficient light on the remarkable conditions which here appear to- 

 be presented to us. 



The Enteron. 



Chilopoda. The nutritive yolk upon which the germ-band lies is 

 very large in Geophilus, and the yolk-pyramids are retained for some 

 time (Fig. 112 A, d). In it lie the nuclei, which are assumed to 

 have remained from the first in the yolk. These nuclei become 



1M2. 



-O.SQ 



Fig. 124.- Sagittal section of an older embryo of Geophilus ferrugineus (after Sograff). 

 a, anus ; bg, ventral chain of ganglia ; d, yolk ; dz, yolk-cells ; ect, ectoderm ; ed, procto- 

 daeum ; h, heart ; ra, mouth ; md, enteron, the development of which is not yet completed, 

 the epithelium being still wanting anteriorly ; rues, mesoderm, partly covering the intestine, 

 partly distributed in the body-cavity ; v.sg, supra-, o.sg, sub-oesophageal ganglion ; vd, 

 stomodaeum. 



arranged into a regular peripheral layer, and gradually the yolk 

 becomes differentiated round each of them to form cell-areas (Fig. 

 121). The demarcation of the cells thus arises, and the enteron 

 is formed (Sograff). "Whether this differentiation takes place in 

 one definite direction, i.e., from before backward, cannot be clearly 

 made out from Sograff's description, but Fig. 124 plainly indicates 

 a progressive development of the enteron from behind forward. 

 The large bulk of the nutritive yolk still remains for some time lying 



