P1ITLLOPODA. 



417 



strongest. In other cases a pair of fin-like appendages are present 

 constituting the caudal fork (Branchipus'). 



Appendages. On the head there are two pairs of antennae, which 

 however, in the adult animal, may be rudimentary or peculiarly 

 modified. The anterior antennae are small, and bear the delicate 

 olfactory hairs. The posterior antennae frequently have the form 

 of large biramous swimming appendages, but in the male may also 

 have a prehensile function, 

 e.g., Branchipus. In other 

 cases (Apus) they are rudi- 

 mentary and may even be 

 enirely absent. 



Two large mandibles are 

 always present beneath 

 the well developed upper 

 lip; they possess a toothed, 

 biting edge, and in the 

 fully developed condition 

 are invariably destitute of 

 palps. The mandibles are 

 followed by one or two 

 pairs of slightly developed 

 maxillae. A kind of under- 

 lip is in many cases present, 

 in the form of two promi- 

 nences behind the mandibles 

 The legs, which are placed 

 on the thorax, are usually 

 very numerous, and are 

 smaller towards the poste- 

 rior end of the body. They 

 are lobed, leaf-like, bira- 

 mous structures, and func- 

 tion as swimming feet ; 

 they also assist in procuring 

 food. They consist of the 

 following parts: a short basal portion, which is usually provided with 

 a masticatory process and is followed by a long foliaceous stem with 

 setae on its inner edge ; this is continued into the multilobed internal 

 branch [endopodite] of the biramous limb, while it bears on its outer 

 de the external ramus [exopodite] with marginal setee, and nearer 



27 



FIG. 333. Male of Branchipus stagnallg. Eg, Heart 

 or dorsal vessel with a pair of slit-like openings 

 in each segment ; D, intestine ; M t mandible ; Sd, 

 shell gland; Br, branchial appendages of the 

 eleven pairs of legs ; T, testis. 



