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 
Fic, 105.—Diacram oF SacitraL Mepian SEction THROUGH A, Limutvs, B, 
HLURYPTERUS. 
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 Hurypterus Fischeri, which are obtainable at 
Rootzikiill, 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 (Znd., Fig. 105, B) situated 
