980 



Tubulation, auxiliary processes of, 461 

 epidermal, 474, 476 

 immediate processes of, 460 

 in Amphioxus, of neural, epidermal, en- 

 todermal and mesodermal organ- 

 forming areas, 494 

 influences which play a part in, 512 

 of entodermal area, in Amphioxus, 500 

 of major organ-forming areas, starting 



point for, 459 

 of mesoderm, in Amphioxus, 503 

 of the mesodermal areas, 490, 492 

 primary, of primitive vertebrate body, 



456 

 processes concerned with, 460 

 Tubules, rete, 15, 16 

 seminiferous, 15 



and response to follicle stimulating 

 hormone (FSH), 24-25 

 straight (tubuli recti), 15, 793, 794 

 Tubuli contorti, 793 

 Tubuli seminiferi, 15 

 Tunica albuginea, 13, 58, 792 

 Tunica dartos, 12 

 Tunica vaginalis communis, 13 

 Tunica vaginalis internus, 13 

 Tunica vaginalis propria, 13 

 Tunicata, xv 

 Turner, C. D., 37 

 Turner, C. L., 27, 197 

 Turtle, carapace formation in, 569 

 development of skin of, 569 

 female reproduction of, 192 

 gastrula of, transverse sections, 420 

 stages in development of, 479 

 surface views of blastoderm of during 

 gastrulation, 418 

 Twin embryos, production of in Amphi- 

 oxus, 335 

 Twinning, in teleost fishes, 382, 386 

 true, in teleost fishes, 386 

 requisite conditions for, 380 

 Twinning conditions, experimentally pro- 

 duced, 381 

 Twins, dizygomatic, definition of, 380 



fraternal, 380 

 Tyler, A., 225, 228 

 Tympanic membrane, internal, 851 

 Tympanum, 851 



U 

 Ultimobranchial bodies, 619, 878, 880 

 Umbilical arteries, 762 

 Umbilical cord, 912, 922 

 Umbilical ring (Umbilicus), 912 

 Umbilical veins, 730 



Umbilicus, 462, 912 



inferior, of feather shaft, 571 

 superior, of feather shaft, 571, 578 

 Unfertilized egg, oxygen consumption of, 



222 

 LJnguiculata, xx 

 Unguis, 584 

 Vngulata, xx 



Unipotency, definition of, 377 

 Unmyelinated (Remak's) fibers, 820 

 Ureter, 788 



Urethra, cavernous, 20, 802 

 Urinary bladders, 787 

 Urinary ducts, 787 



development of in vertebrates, 798 

 types of, 787 

 Urinary recess, 803 

 Urochordata (Tunicata), subphylum, xv 



asexual reproduction in, 53 

 Urodela, xvii 



Cryptobranchus alleganiensis, testis in 

 relation to reproductive ducts, 19 

 Necturus maculosus, reproductive struc- 

 tures of, female, 63 

 saccular ovary of, 62 

 testis in relation to reproductive ducts, 

 19 

 neotropical, Oedipus, sperm transpc?rt in 



female, 191 

 sperm of, 143 

 spermatophores in, 21 

 Urogenital mesoderm, synonymous with 



mesomere, 492 

 Urogenital opening, of mammals, 715 

 Urogenital sinus region, 787 

 Urogenital structures, differentiation of in 

 human embryo, 788 

 embryonic tissues which contribute to, 

 772 

 Urogenital system, definition of, 769 



relationships in various vertebrates, 782 

 Urogenital union, 794 

 Uromastix hardwicki, developing egg of, 



167 

 Uropygial glands, in bird, 571 

 Urorectal folds, 787 

 Urostyle, 686 

 Uterine cycle, 92 

 Uterine horn, anterior end of, in opossum, 



194 

 Uterine segments, of oviduct, degrees of 



fusion of, 64 

 Uterine tube, in rabbit, peculiar behavior 



in sperm transport, 193 

 Uterus, 64 



a preformationist conception of, 56 

 development of, 802 



