mxl 



Kt 2 



FIG. 43. Sagittal section of a young scorpion (arachnid) to be compared with 

 fig. 44. c. a, carotid artery; ch, cerebral hemispheres; e. t, parietal eye tube; 

 ht 2 -ht 3 , heart; 1. e. g, lateral eye ganglion; mxl, maxillaria; ra, mouth; nch, noto- 

 chord; oc. r, occipital region; pae. g, parietal eye ganglion; ro, rostrum; st. co, 

 stomodaeal commissure. (After Patten's " Evolution of the Vertebrates and their 

 Kin " [P. Blakiston's Sons and Co.].) 



ctt 



pde. A; ch. ol.l. 



FIG. 44. Sagittal section of a primitive vertebrate embryo, showing the rela- 

 tion of its principal organs to those in the arachnids (cf. fig. 43); schematic, a. np, 

 anterior neuropore; 6. nv, belly navel; cbl, cerebellum; C. d, duct of Cuvier; 

 ch, cerebral hemispheres; cnv, new ventral mouth; et, eye tube; hy, hyoid; I, lung; 

 m, mouth; oe, oesophagus; ocr, occipital region; oL I, olfactory lobe; op. I, optic 

 lobe; pa..e, parietal eye; pit, pituitary body; pr.mx, premaxilla; md, mandible; 

 mx, maxilla; S, stomach; s. v, sinus venosus; v, ventricle. (From Patten's " Evolu- 

 tion of the Vertebrates and their Kin " [P. Blakiston's Sons and Co.].) 



81 



