53 6 THE ORIGIN OF VERTEBRATES 



Thelyphonus, operculum, 189, 190, 206, 207 

 Theory, gastraa, 444, 461 



Theories of the origin of vertebrates, 9, 411, 433, 457 

 Thionin reaction, 131, 139, 213, 330, 336 

 Throat, formation of, 179 



Thyestes, 30, 31, 275, 326, 328, 329, 339, 340, 341 

 Thymus, 425, 430 



Thyroid gland of Ammoccetes, 61, 127, 192, 194, 196, 429, 459 

 „ „ evidence of the, 185 



n ,, function of, in Ammoccetes, 213 



Tissues, connective, 471, 474, 481 

 „ evolution of, 19 

 ,, notochordal, 435 

 ,, two groups of, 463 

 Tongue of Ammoccetes, 246, 303 

 Tonsils, 427, 430 

 Torpedo, 262, 392, 470 

 Trabecule, 121, 132, 133, 145, 277, 295, 377 

 Transformation of the Lamprey, 18, 35, 59, 61, 125, 168, 193, 199, 200, 220, 227, 228, 



287, 291, 304, 307, 309, 331, 336, 347, 349, 389, 445 

 Tremataspis, 32, 75, 275, 326, 351, 352 

 Trilobites, 24, 25, 26, 437 



appendages, 351, 437 



diagram of section through a trilobite-like animal, 413 

 dominance of, 26 

 excretory organs, 396 

 eyes, 74, 88 

 glabellum, 339 

 relations of, 249, 283 

 respiratory apparatus, 170 

 ventral surface, 437 

 Tube of central nervous system, 37, 38, 42, 102, 211, 433, 455, 457 

 ,, from IVth ventricle to surface of brain in Ammoccetes, 209 

 ,, Fallopian, 431 

 „ hypophysial, 229, 244, 317, 440 

 „ meeting of four tubes in vertebrate, 318, 440 

 ,, notochord originally a, 436, 440 

 ,, olfactory, of Ammoccetes, 219, 225, 317, 440 

 ,, unsegmented, in segmented animal, 439 

 Tunicata, 16 



,, budding of, 441 



degeneration, 12, 17, 19, 60 

 endostyle, 198, 212 

 ,, hypophysis, 425 

 ,, notochord, 438 

 ,, position of, 494 



Unit, appendage, in non-branchial segments, 185 



„ branchial, 161, 165, 168, 185 

 Ureters, nerves of, 448 

 Uterus of Scorpion group, 189, 202, 203, 204, 205, 214 



„ vertebrate, nerves of, 448 



