222 



THE ORIGIN OF VERTEBRATES 



cam 



pr.ent 



character is, of course, evident enough, for it is innervated by a pair of 

 nerves, and these nerves, as ought to be the case, arise from the supra- 

 oesophageal ganglia. In Galeodes it is a conspicuously paired antennae- 

 like organ (Fig. 94). 



Croneberg has also shown that this rostrum, or camerostome, arises 

 embryologically as a pair of appendages similar to the other append- 

 ages. This last observation 

 of Croneberg has been con- 

 firmed by Brauer in 1894, 

 who describes the origin of 

 the upper lip, as he calls it, 

 in very similar terms, with- 

 out, however, referring to 

 Croneberg's paper. Crone- 

 berg further shows that this 

 foremost pair of antennas 

 not only forms the so-called 

 upper lip or camerostome, 

 but also a lower lip, for 

 from the basal part of the 

 camerostome there projects 

 on each side of the pharynx 

 a dependent accessory por- 

 tion, which in some cases 

 fuses in the middle line, and 

 forms, as it were, a lower lip. 

 The entosclerite belonging 

 to this dependent portion is 

 apparently the post - oral 

 entosclerite of Lankester and 

 Miss Beck. 



At the base of the tubular 

 passage formed by this modified first pair of antennas the true mouth 

 is found opening directly into the dilated pharynx, the muscles 

 of which enable the act of suction to be carried out. The narrow 

 oesophagus leads out from the pharynx and is completely surrounded 

 by the supra- and infra-oesophageal nerve masses. 



Huxley also describes the mouth of the scorpion in precisely the 

 same position (cf. o, Fig. 96). 



Fig. 94. — Dobsal View of Brain and Came- 

 rostome op Galeodes. 



cam., camerostome; pr. ent., pre-oral entoscle- 

 rite ; l.l., dependent portion of camerostome ; 

 ph., pharynx; al., alimentary canal; n. op., 

 median optic nerves; pi., plastron; v.c, 

 ventral nerve chain ; 2, 3, second and third 

 appendages. 



