224 



THE ORIGIN OF VERTEBRATES 



Croneberg's observatiuns and conclusions are distinctly of very 

 groat importance in bringing the arachnids into line with the crus- 

 taceans, and it is therefore most surprising that they are absolutely 

 ignored by Lankester and Miss Beck in their paper published in 

 1883, in which Latreille only is mentioned with respect to this 

 organ, and his term " camerostome," or upper lip, is used throughout, 

 in accordance with the terminology in Lankester's previous paper. 

 That this organ is not only a movable lip or tongue, but essentially 

 a sense-organ, almost certainly of smell and taste, as follows from 

 Croneberg's conclusions, is shown by the series of sections which I 

 have made through a number of young Thelyphonus (Fig. 102). 



pr em 



. / Hyp 



Olf pass 



Fig. 96. — Median Sagittal Section through a Young Thelyphonus. 



I give in Fig. 96 a sagittal median section through the head-end 

 of the animal, which shows clearly the nature of Croneberg's con- 

 ception. At the front end of the body is seen the median eye (cc), 

 u is the mouth, Ph. the pharynx, ces. the narrow cesophagus, com- 

 pressed between the supra-oesophageal (swpr. ces.) and infra-cesopha- 

 geal (infr. ces.) brain mass, which opens into the large alimentary 

 canal (A I.) ; Olf. pass, is the olfactory passage to the mouth, lined 

 with thick- set, very fine hairs, which spring from the hypostome 

 (Hyp.) as well as from the large conspicuous camerostome (Cam.), 

 which limits this tube anteriorly. The space between the came- 

 rostome and the median eye is filled up by the massive chelicerse, 

 which are not shown in this section, as they begin to appear in the 



