THE CYCLE OF LIFE 421 



gradually and by various routes. Thus we see a beginning 

 in those cases in which the mother lays her eggs, instead 

 of merely liberating them. The female salmon lays eggs 

 in a furrow which she makes in the gravelly bed of the 

 stream. We see a beginning in those cases in which the 

 mother carries her eggs about with her after she has liberated 



FIG. 64. Female Spider Dolomedes mirabilis carrying underneath 

 her body, attached by silk threads, the silken cocoon containing 

 the eggs and eventually the young spiders. (After Blackwall.) 



them. Many a spider has a silken cocoon which she bears 

 about with her until the spiderlings hatch. We see a 

 beginning in the retention of the eggs, not only until they 

 become larvae, but until particular circumstances arise. 

 Thus the freshwater mussel, which we have discussed, 

 keeps its Grlochidia in its gill-cradle until a minnow or 

 the like comes conveniently into the vicinity. We see 

 a beginning in the way many an animal mother allows her 

 young ones to clamber about her body, holding on to her 

 and being protected by her. The generalization may be 



