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- 

 dividual can transmit must be represented in its germ cells. 

 (Figs. 8, 28, 180.) 



