. The development of the chick; an introduction to embryology . ughter-chromosomes diverge towards opposite polesof the spindle. The outer end of the second maturation spindlethen enters a superficial bud of the protoplasm of the germinaldisc similar to that of the first maturation spindle; and this budtogether with the contained chromosomes becomes cut off as thesecond polar body. The result of these processes of maturation is the formationof three cells, viz., the two polar bodies and the mature polar bodies are relatively very minute and soon degeneratecompletely. After the formatio
. The development of the chick; an introduction to embryology . ughter-chromosomes diverge towards opposite polesof the spindle. The outer end of the second maturation spindlethen enters a superficial bud of the protoplasm of the germinaldisc similar to that of the first maturation spindle; and this budtogether with the contained chromosomes becomes cut off as thesecond polar body. The result of these processes of maturation is the formationof three cells, viz., the two polar bodies and the mature polar bodies are relatively very minute and soon degeneratecompletely. After the formation of the second polar body there remainin the egg eight chromosomes, each of which represents onequarter of an original tetrad. These form a small resting nucleusknown as the egg-nucleus or female pronucleus. It is manytimes smaller than the original germinal vesicle (Fig. 12), and DEVELOPMENT PRIOR TO LAYING 35 it rapidly withdraws from the surface of the egg to a deeperposition near the center of the germinal disc. (Concerning the ~ -py.^.. Fig. 12.— Egg nucleus (female pronucleus) and polar bodies of the pigeons egg. (After Harper.) x 2000. E. N., Egg nucleus, p. b. 1, First polar body. p. b. 2,Second polar body. pv. S., Perivitelline space, v. M., Vi-telline membrane. general theory of the maturation process see E. B. Wilson, TheCell in Development and Inheritance/ the Macmillan Company,New York.) 11. Fertilization The spermatozoa traverse the entire length of the oviductand are found in the uppermost portion in a fertile hen. Theperiod of life of the spermatozoa w^ithin the oviduct is considerable,as proved by the fact that hens may continue to lay fertile eggsfor a period of at least three weeks after isolation from the the end of the third week the vitality of the spermatozoais apparently reduced, as eggs laid during the fourth and fifthweeks may exhibit, at the most, abnormal cleavage, which soonceases. Eggs laid forty days after
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