999 







MYRIOPODA. 



most part the entoderm, but is also said to take part in the formation 

 of the mesoderm (Sograff, Heathcote). The latter arises partly as 

 a cell-growth which takes place in the ventro- median portion of 

 the blastoderm. There arises in this region a thickening of the 

 blastoderm projecting inward in the shape of a keel (Fig. 108), in 

 the formation of which cells are said to take part that migrate from 

 the inner part of the egg and become applied to the thickening 

 (Heathcote, Sograff). This thickening is at first median, but 

 divides later into two lateral bands (the mesoderm-bands), which 

 then break up into segments containing cavities. 



— mXi 



Fig. 109.— Surface views of three early stages in the development of Geophilus ferrugineus, 

 showing the rudiment of the germ-band (after Sograff). A and C, lateral views. C, ventral 

 view of the anterior part of the germ-band, a, anus ; at, antenna ; d, yolk ; Tel, cephalic 

 lobes; md, mandibular segment; mx lt segment of the first pair of maxillae ; r, median 

 longitudinal groove. 



AsJ a longitudinal furrow appeared early in the ventral middle 

 line, the formation of the germ-bands in the Myriopoda might be 

 interpreted in the same way as in Perijxdus, i.e., the furrow might 

 be regarded as an indication of gastrulation, especially as the mouth 

 and the anus appear at its anterior and posterior ends. 



This view, indeed, is in opposition to the statements regarding the origin of 

 the entoderm from cells which have remained in the yolk, but we must remember 



