240 



THE ORIGIN OF VERTEBRATES 



between the basal joints of all the pairs of locomotor appendages 

 could be closed from behind. Woodward says it no doubt represents 

 the labium, and served more effectually to enclose the posterior part 

 of the buccal orifice, being found exteriorly to the toothed edges of the 

 ectognaths or maxillipedes. Schmidt agrees with Nieskowski, and 



M.obl. 



Fig. 105. — Diagram of Sagittal Median Section through A, Limulus, B, 



Eurypterus. 



looks on the mestasoma as forming a lower lip within which the 

 bases of the ectognaths worked. 



Quite recently Gerhard Holm has worked over again the very 

 numerous specimens of Eurypterus Fischeri, which are obtainable at 

 Rootzikull, and has thrown new light on the relation of the metas- 

 toma to the mouth-parts. His preparations show clearly that the 

 true lower lip of Eurypterus was not the metastoma, for when the 

 metastoma is removed another plate {End., Pig. 105, B) situated 



