PI.ATY! I. \l IN I III S. 



201 



of which be- 

 very thin 



Two pairs of imaginations of the skin, just as in the type of 

 Desor, now make their appearance, one pair in front of and the 

 other tehirul the mouth (fig. 93 B, f>r.d, and jw.d.), and each of 

 them by the closure 

 of the opening of 

 invagination forms 

 a sack, the outer 

 wall 

 comes 



and the inner 

 wall (correspond- 

 ing with the whole 

 invagination of the 

 type of Desor) very 

 thick. The inner 

 walls of the four 

 thickenings, which 

 I may speak of as 

 discs, now fuse to- 

 gether, each disc 

 first uniting with 

 its fellow, 

 finally the 

 pairs uniting. 



A ventral ger- 

 minal plate is thus 

 established, which 

 gradually grows Fl(: . 94 . 



A. PlUDIUM WITH AN A0\ ANrf.n NKMF.RTINR 

 WORM. 



I!. RlPE EMBRYO OF THE NEMERTKA IN THE 

 POSITION IT OCCUPIES IN I'llllHI'M. (Both after 

 Biitschli.) 



or. oesophagus ; it. stomach ; i. intestine ; fr, pro- 

 boscis ; //. lateral pit ; an. amnion ; H. nervous system. 



thin layer of each of the discs grows fan fassu with the inner 

 layer, and furnishes an amnion-likc covering for the embryo 

 which is forming within the Pilidium (fig. 94, an}. 



In connection with the young vermiform Ncmcrtinc thcr 

 formed on each side an outgrowth from the oesophagus (fig. 94) 

 which is eventually placed in communication with the exterior 



and 

 two 



round the intestine 

 of the Pilidium to 

 form the skin of 

 the future Nemcr- 

 tine. The outer 



