SECT, in THE APPENDAGES 41 



in addition to the masticatory ridge or ventral para- 

 podium. In the Eurypteridae, the ventral masticatory 



part seems to have almost disappeared in Pterygotus, 

 (see Fig. 55, p. 239) but to be well developed in 

 Eurypterus (Fig. 56, p. 245). 



V. The Second Maxilla- -This much-discussed 

 limb has retained rather a larger rudiment of the 

 dorsal parapodium than the first maxilla ; in it, in 

 fact, the dorsal is the more important of the two 

 branches, the ventral being rendered almost useless 

 by the powerful first maxilla, between which and 

 the ventral parapodium of the first trunk limb it 

 is squeezed (sec Fig. 2 and Frontispiece). The 

 dorsal parapodium is reduced to a stump without 

 appendages, but is interesting on account of the 

 aperture of the shell gland at its tip ; we are thus 

 able, as already mentioned, to homologise the shell 

 gland with the setiparous sac of the original An- 

 nelidan parapodium (see section on Excretion, also 

 Fig. I, p. 12). The opening of the shell gland on 

 this limb shows it to be the second maxilla, and not 

 a maxillipede, as some authors maintain. An ex- 

 amination of the musculature shows further that this 

 limb belongs to the fifth segment, a long thin muscle 

 band descending into it from in front of the opening 

 of the shield, which is a fold of the dorsal integu- 

 ment of this segment. This muscle band is doubt- 

 less homologous with the bands which, in each 

 segment, run from the dorsal integument into its 

 limb (see Figs. 14, p. 59, and 15, p. 60). 



The five limbs just described are the typical five 



