966 



Organization center, 398 



characteristics of, 399 



different action of compared to ordinary 

 induction of neural tube, 400 



dual appearance of in trout blastoderm, 

 382 



importance of, 395 



in late blastula, 283 



isolation of in early duck embryo, 385 



necessity for, 381 



of late blastula, importance of, 386 



relation of to gastrulative process, 398 

 Organizers, xii 



primary, importance of, 395 

 Organogenesis, definition of, 518 

 Origin of germ cells, 12 It 

 Ornithorynchus paradoxus, xx 

 Oryctolagus cuniculus (rabbit), character- 

 istics of egg, site of fertilization, 

 and place of sperm entrance into 

 egg, 206t 

 Ossification, centers of, 695 



of bony skulls, 674 

 Osteoblasts, 666, 693 



in developing scale of Lepisosteus, 563 

 Osteoclast, 661, 693 



action of in bone formation, 667 

 Osteocollagenous fibers, 659 

 Osteocytes, 659, 662, 666 

 Ostium tubae abdominale, 63 

 Ostrea virginica, spawning reaction in, 230 

 Otic capsules, 671 

 Otic ganglion, association with parotid 



gland, 831 

 Otic placodes, 850 

 Otic vesicle, differentiation of, 830 

 Otoliths, of ear, 854 

 Ova, degeneration of, 67 

 Ovarian capsule, around ovary of rat, 194 

 Ovarian cycle, 92 



Ovarian fertilization, in eutherian mammal, 

 Ericulus, 197 



in Gambusia affinis, 197 



in Heterandria fonnosa, 197 

 Ovarian ligament, 803 

 Ovarian sac, 799 



Ovariectomy, during pregnancy, 99 

 Ovaries, 788 



activities of, 67 



as dynamic center of reproduction for 

 most animal species, 56 



as source of estrogen, 86 



as "storehouse" of oogonia, 67 



bird ovary, 61 



cortex of, 58, 67, 68 



cyclic changes in, 60 



development of, in chick, 797 

 in mammal, 795 



Ovaries — (Continued) 



effects of vitamin deficiency upon, 66 



fertilization in, 197 



general cell structure of, 60 



germinal epithelium of, 58 



hilus of, 58 



human, development of, 797 



importance of, 53 



importance of in mammary gland devel- 

 opment and lactation, 103 



internal conditions as an ovulatory 

 factor, 81 



medulla of, 58 



of the hen, estrogenic hormone in, 73 



other possible functions of, 108 



relation of to infundibulum, in opossum, 

 194 



role of in gestation, 98 



role of in parturition, 101 



saccular, 60, 62 



structure in teleosts, 59 



structure of, 57 



tunica albuginea of, 58 



use of words, 5 

 Oviduct, glandular portion of, 62 



of birds, albumen-secreting region of, 

 905 



ostium of, in Rana pipiens, 195 



uterine portion of, 62 



protective function of, 901 



uterine segments of, degrees of fusion of, 

 64 

 Oviparity, 903 



Oviparous, definition of, 903 

 Ovis aries (sheep), characteristics of egg, 

 site of fertilization, and place of 

 sperm entrance into egg, 207t 

 Ovists, 56 

 Ovotestis, 890 

 Ovoviviparity, 903 

 Ovoviviparous species, 902 

 Ovulation, dependent, 82 



factors controlling, 75 



hormonal control of, in lower verte- 

 brates, 80 



in lower vertebrate groups, 79 



in the hen, role of progestrone, 80 



in the rabbit, 77 



internal conditions of the ovary as a 

 factor, 81 



process of in higher mammals, 76 



spontaneous, 82 

 Ovulatory process, hormonal control of, 78 

 Ovum, definition, Harvey's conception of, 



55 

 Owen, R., 536 



