EXTREMITIES. 



295 



and it has recently been observed by Ntjsbat/M (Xo. 63) in Meloe. This 

 structure may best be compared with the paragnatha of the Crustacea, although 

 we are apparently precluded from homologising it with this latter. 



C. Extremities. 



The limbs appear as sac-like swellings of the surface of the 

 segments, which, as a rule, are directed backward. The antennal 

 rudiments must be regarded as the most anterior pair of true limbs ; 

 this belongs to the cephalic region, and arises near the posterior 

 edge of the cephalic lobes, at the point where these pass into the 

 mandibular segment (Figs. 146, an, and 147, at). It should be 

 specially pointed out that the antennal rudiment, even when it first 

 appears, is, as Weismanx (No. 87) has shown, post-oral in position 

 (Fig. 147, at) and 



Jl. 



JJ. 



,vft 



se- 



9 — 



shifts towards the 

 mouth only later, 

 finally coming to 

 lie in front of or 

 above it. The an- 

 tennal rudiment, 

 in its external 

 appearance, de- 

 velopment, and 

 position closely re- 

 sembles the other 

 limb-rudiments. 



Weismann's im- 

 portant discovery 



that the antennal 

 rudiment is origin- 

 ally post-oral in 

 position has recently 

 been confirmed by 

 various observers 

 (Graber, No. 25, 

 and Heider, No. 38, 

 for Hy d r op hilus ; 

 Patten, No. 67, for 

 A ciliu s ; G R A i; E B , 



No. 30, for Stcnobothrus, Lepidoptera, Hylotoma ; Nusbavm, Xo. 63, for Meloe ; 

 WHEELER, Xo. 95, for Doryphora ; CARRIERS, Xo. 13, for Chalicodoma, etc.). 

 This position, as well as the agreement in form between the antennal rudiment 

 and the other limbs, lends important support to the view we have already 

 expressed in connection with Peripatus (p. 186, etc.), and which also applies to 

 the Insecta, that the antennae are structures secondarily shifted to a position in 



Fig. 146.— Embryos of Hydrophilus with limb-rudiments (after 

 Heider, from Lang's Text-book), a, anal aperture ; an, antenna ; 

 g, rudiment of the ventral chain of ganglia ; m, oral aperture ; 

 md, mandible; mx lt first, mx„, second maxilla; pi, p-, j^\ the 

 three pairs of thoracic limbs ; pi, pi, p<, p9 ( rudiments of the 

 first six abdominal limbs ; st, stigmata ; vk, procephalon. 



