192 THE APODIDyE part ii 



ventral parapodium being only occasionally retained 

 as a mere rudiment. This very striking difference 

 between Apus and Limulus is thus at the same time 

 a link, since it connects them both with our Crustacean 

 Annelid. 



The sixth pair of limbs has already been homologiscd 

 with the first trunk limbs of Apus and the other Crus- 



e^-^ 



Fig. 44.^— Basal part of one of the 2nd pairs of limbs o{ Li»iidns iiiohiccanus{{ro\\\. 

 Bronn's Klasseti ntid Ordnnngcn dcs Thierrciches) to show the well-developed 

 ventral parapodium, retaining the remains of its sensory cirrus (c) ; d, dorsal 

 parapodium ; 7', ventral parapodium. 



tacea. It differs characteristically from the head 

 appendages. Its ventral parapodium is well developed 

 as a masticatory ridge, and functions as a jaw, in front 

 of the under lip, with the masticators of the last four 

 head segments. Its dorsal parapodium, however, is 

 developed in a peculiar way. It is a powerful limb for 

 pushing the animal forward in its burrowing operations ; 

 its tip is provided with a group of sensory feelers 



