. Animal biology. Biology; Zoology; Physiology. 284 ANIMAL BIOLOGY more proof of the indebtedness of the 'practical man of affairs' to the biological laboratory. In the Protozoa the problems of heredity confront us in their sim- plest, though by no means simple form. Amoeba or Paramecium, as we know, divides into two cells which through growth and reorganization soon are to all intents and purposes exactly similar to the parent cell. The par- ent has merged its individ- uality into that of its off- spring. Thus stated, one does not wonder that par- ent and offspring are alike — each is compose
. Animal biology. Biology; Zoology; Physiology. 284 ANIMAL BIOLOGY more proof of the indebtedness of the 'practical man of affairs' to the biological laboratory. In the Protozoa the problems of heredity confront us in their sim- plest, though by no means simple form. Amoeba or Paramecium, as we know, divides into two cells which through growth and reorganization soon are to all intents and purposes exactly similar to the parent cell. The par- ent has merged its individ- uality into that of its off- spring. Thus stated, one does not wonder that par- ent and offspring are alike — each is composed of es- sentially the same proto- plasm. But when we come to multicellular forms in which reproduction is re- stricted to special germ cells which involve ferti- lization, confusion is apt to arise unless one keeps clearly in mind - - and per- haps exaggerates for the sake of concreteness — the distinction between germ and soma which has been previously discussed. Since in higher forms, to which brevity demands that our attention be confined, the. Germ Soma Fig. 180. — Scheme to illustrate the con- tinuity of the germ. Each triangle repre- sents an individual composed of germ (dotted) and soma (clear). The beginning of the life cycle of each individual is at the apex of the triangle where both germ and soma are present. In biparental (sexual) reproduction the germ cells of two individ- uals become associated in a common stream which is the germ and gives rise to the soma and germ of the new generation. This con- tinuity is indicated by the heavy broken line and the collateral contributions at each suc- ceeding generation by light broken lines. (From Walter.) sole connection between parent and offspring is through the germ cells, it follows that they must be the sole path of inheritance. In other words, whatever characters the body actually inherits must have been represented by genes in the fertilized egg from which it arose; and furthermore, any characters which the in-
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