956 



Hypophysis, and relation to testicular func- 

 tion, 39 

 anterior lobe, results of removal, 39 

 structural composition of, 39 

 structure of in various vertebrates, 877 

 Hypophysis cerebri, 39, 876 {see also Pi- 

 tuitary gland) 

 Hyporachis (aftershaft), 571, 578 



I 



Ichthyopterygium (a type of bilateral ap- 

 pendage), 691 

 Identical (monogametic) twins, definition 



of, 380 

 Idioplasm theory, of Nageli, 215 

 Idiosome (idiozome), description of, 126 



nature of, 126 

 Ilium, 693 

 Implantation, definition of, 916 



in Macaca rnulatta (rhesus monkey), 



922 

 in monkey, 919 

 of human embryo, 918, 919 

 of pig embryo, 923 

 types of, 916, 917 

 Inactive fertilizin, 269 

 Incisor teeth, 607 

 Incremental cone, of developing neuroblast 



fiber, 808 

 Incus, 674, 851 

 Individuation, definition of, 378 



of specific organ-forming territories, a 

 main function of the gastrulative 

 process, 447 

 processes involved in, 379 

 Induction, 400 



of a secondary embryo, 411 

 Inductors, xii 



Inferior caval veins, of chick embryo, 746 

 Inferior vena cava, 740 

 Infundibula (vestibules) of chick's lung, 



647 

 Infundibulum, 822 



relation of to ovary, in opossum, 194 

 Ingalls. N. W., 721 

 Ingression, during gastrulation, definition 



of, 397 

 Inguinal fold, 1 1 



Inguinal ligament, of mesonephros, 803 

 Inner cell mass embryonic knob, 300, 303 

 Inner ear, 851. 854 



Innervation, dual, of autonomous nervous 

 system, 836 

 of premuscle masses in head and pha- 

 ryngeal areas, 720 

 Insectivora, xx 



Insemination, artificial, of human female 

 and domestic animals, 199, 229 



Insulin, 875 



Integument, vertebrate, definition and gen- 

 eral structure of, 556 

 origin of component parts of, 557 

 Interatrial opening, of developing mam- 

 malian heart, 757 

 Interatrial septum, of developing heart, 



753, 754, 757 

 Interbasalia, 685 

 Intercalated discs, of cardiac muscle, 701, 



704 

 Intercoelomic membrane, 506 

 Intercostal arteries, 760 

 Interdorsals, of arcualia, 682, 685 

 Interkinesis, 131, 132 



Intermediate cell mass, synonymous with 

 mesomere and intermediate meso- 

 derm, 492 

 Internal ear, development of, 855 

 Internal migration, of egg, in frog, 201 

 Internal transverse muscle, of frog, 707 

 Internodel segment, of peripheral nerve 



fibers, 819 

 Interoceptive field, 842 

 Interparietal bone, 695 

 Intersegmental veins, of chick embryo, 743 

 Intersexes, 889 



Interstitial tissue, of testis, 793 

 Interventrals, of arcualia, 682 

 Interventricular septum, of developing 



heart, 753. 754, 757 

 Intervertebral disc, 682 

 Intestinal folds, 632 

 Intestinal vein, 736 



Intestine, anterior area, diverticula of, 601 

 histogenesis of, 631 

 morphogenesis of, in various vertebrates, 



630 

 small, 630 



torsion and rotation of. 630 

 Intrinsic ganglia, of autonomic nervous 



system, 837 

 Intromittent organ, development of, 802 

 in Ascaphus truei, 190 

 in male fishes, 755 

 of gymnophionan amphibia, 792 

 Invagination, definition of, in gastrulation, 



390, 397 

 Involution, definition of, during gastrula- 

 tion, 396 

 Iris, development of, 845 

 Irritability, 807, 814 

 Ischium, 693 

 Isotropic substance, 703 

 Isthmus, of bird oviduct, albumen addition 

 to egg in. 906 {see also Fig. 157) 

 Isthmus, of thyroid gland, 877 

 Ivy, A. C, 892 



