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| showing a large distinct nucleus containing a small, dark, spherical nucleolus |
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| a one-celled stage but too opaque to show a nucleus; may be distinguished from blastula due to its being solid and therefore darker than the blastula |
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| composed of 2 equal and very evident cells |
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| composed of four smaller but evident cells |
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| a solid sphere of eight cells |
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| 3 days of development; ball of cells |
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| hollow sphere stage in which the cells form a single layer called the blastoderm; the lighter cavity is called the blastocoel |
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| hollow but with one side invaginated (pushed in); ectoderm, mesoderm, endoderm forming |
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| includes the whole complex embryo and extra-embryonic membranes |
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| outer extra-embryonic membrane of the chorionic sac; part is thin at either end, whereas the middle portion is a thick band--this representst the cat's fetal placenta |
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| delicate, transparent membrane close to the developing cat; between this structure and the developing cat is the amniotic fluid which prevents embryonic dessication and also prevents the embryo from sticking to surrounding tissues |
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| links developing cat to the placenta; within this structure are the umbilical vein (carries oxygen and nutrients from placenta to the embryo) and two umbilical arteries (carries wastes such as urea and carbon dioxide from the embryo to the placenta); ceases to function at birth |
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| spot on the abdomen where the umbilical cord would be attached to the cat |
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| first evident in 18-hr chick; light central area; region which is free from underlying yolk; area where embryo will develop |
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| first evident in 18hr chick; marginal darker area; representing area attached to the yolk |
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| first evident in 18hr chick; longitudinal groove bordered by 2 ridges; located in the area pellucida; with continued incubation the embryo will develop in front of this streak |
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| first evident in 24hr chick; laterally placed segments which develop into such things as muscle, vertebral elements, and inner portions of skin; paired along the midline; number will increase with continued development |
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| first evident in 24hr chick; in midline; will become the brain and spinal cord with further development |
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| first evident in 33hr chick; cranial enlargement of the neural tube; forebrain; later gives rise to the telencephalon and diencephalon |
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| first evident in 33hr chick; lateral bulge of the proencephalon; will become the retina of the eye with further development |
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| first evident in 33hr chick; bulblike and immediately behind proencephalon; midbrain |
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| first evident in 33hr chick; narrower than mesencephalon and immediately behind it; provided with a number of minor constrictions; its caudal border is indefinite at this time; hindbrain; later gives rise to metencephalon and myelencephalon |
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| first evident in 33hr chick; saclike structure bulging to the right at the level of the rhombencephalon |
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| first evident in 33hr chick; one on either side behind heart where 2 vessels angle medially and unite; these vessels carry blood into the heart |
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