INTRODUCTION 9 



as temporarily to lose their likeness to the parent 

 generation, although readily regaining that likeness 

 when springtime brings the opportunity. The unity 

 of two succeeding generations, although interrupted 

 by the temporary interposition of something ap- 

 parently different in the form of gemmules or stato- 

 blasts, is thus essentially maintained. The bryozoan 

 colonies of two successive seasons in a fresh-water 

 pond may be regarded as parts of the same identical 

 colony, since they present an "organic resemblance 

 based on descent," although the sole representatives 

 of the parent colony during midwinter may be the 

 sparks of life locked up within the statoblasts buried 

 in the mud. 



Similarly, the asexual spores of many plants, such 

 as molds, mosses and ferns, may be regarded as 

 gemmules reduced to the lowest terms, namely, to 

 single cells. As in the preceding cases so in this 

 instance the resemblance of the offspring which may 

 arise from these spores, to the parents which pro- 

 duced them, is due to the essential material identity 

 of two generations. 



These illustrations of heredity in its simplest mani- 

 festations give the key to "organic resemblance" 

 higher up in the scale. Sexual reproduction is no 

 less plainly the direct continuation of life though in 

 this instance two sporelike fragments out of one 

 generation contribute to form the new individual of 

 the next generation instead of one fragment. In all 

 cases there is a material continuity between succeeding 

 generations. Offspring become thus an extension of 



