Polar

(po/-lar). Pertaining or belonging to the poles. P. Crown, the disc of chromatin grains at each pole of the nuclear spindle in karyokinesis. P. Field, the clear space enclosed by the chromatin -loops of the loose skein, in karyokinesis, and in which the nuclear spindle appears. Cf. Sphere of Attraction, Centrosome. P. Globules, two ma es of nuclear substance detached from the nuclear spindles during karyokinesis. They appear to be nece ary to the complete maturation of the ovum, although they ultimately disappear. Only one polar globule occurs in parthenogenetic ova. They have been described by Fleming in white blood-corpuscles. The significance of the polar bodies is not definitely known. According to certain embryologists the ovum is originally hermaphroditic, the polar bodies representing the male element, which the ovum expels in order to prepare for the entrance of the male pronucleus. An analogous condition, leading also to the lo of certain elements, is thought to exist in the spermatozoon, which likewise is originally hermaphroditic. Weismann looks upon the polar bodies as ma es of ovogenetic nucleoplasm which are expelled from the ovum, in order that the more important germ-plasm may develop actively. The bodies are also known as the polar globules of Robin. P. Method, a method of applying electricity in electro therapeutics, i which n the pole whose distinctive effect is wanted is placed over the part to be treated, and the other pole over some indifferent part. P. Nucleus, in biology, the fourth nucleus in each group at the two extremities of the embryo-sac. P. Reaction, in electricity, the measure of muscular contraction that follows the application of the positive (anode) or negative (kathode) pole to a nerve or muscle. P. Vesicle. Same as P. Globule. P. Zone. See Zone.