226 



MYRIOPODA. 



In the middle of the germ-band a shallow furrow appears (Fig. 

 109 G) extending from the mouth to the anus, the two apertures 

 marking the ends of the furrow (Sograff). This furrow, which 

 soon disappears, naturally invites comparison with the long slit-like 

 blastopore of Peripatus on account of its corresponding position and 

 relation to the mouth and anus (c/. pp. 175 and 222). 



Somewhat later, on each side of the middle line, the rudiments 

 of the ganglionic chain appear as thickenings of the ectoderm also 

 separated by a median furrow (Fig. Ill, nr). This furrow, however, 

 must not be confounded with the furrow just mentioned, which 

 has disappeared before the formation of the groove now under 

 consideration. 



So far the germ-band of Geopliilus, with its numerous segments, 

 has developed from before backward, and extends with a dorsal 

 curvature round the greater part of the yolk-mass (Fig. 112 A). 



The posterior end at a some- 

 what later stage grows even 

 further up on to the dorsal side, 

 so as to approach still more 

 nearly the cephalic lobes, as 

 may be seen in Fig. 112 B. 

 Now, however, a change takes 

 place, a transverse ventral fur- 

 row appearing in the region 

 of the twentieth segment. This 

 furrow deepens considerably 

 (Fig. 113), and finally causes the 

 curvature of the embryo to 

 change completely from a dorsal 

 to a ventral flexure (Fig. 114), 

 This causes the posterior end 

 of the body to separate from 

 the cephalic lobes, and consequently the dorsal surface, which was 

 formerly much shortened, now undergoes extension (Figs. 112 B, 

 113 and 114). The ventral surface of the posterior half of the 

 body now lies exactly opposite to, and parallel with, the anterior 

 half (Fig. 114), so that the tips of the extremities of the one half 

 touch those of the other, and this flexure of the embryo again leads 

 to the approximation of the caudal and cephalic lobes (Fig. 114, 

 M and si). 



Up to this point the actual embryo, as the germ-band, has remained 



Fig. 113. — Embryo of Geophilus ferrugineits at 

 the stage when the germ-band begins to flex 

 ventrally ; seen obliquely from the ventral 

 side (after Soqraff). at, antenna ; d, yolk ; 

 el , point at which the band bends ; ex, limbs ; 

 lest, germ-band. 



