24 PLANT-ANIMALS [CH. 



of slack tides when the paradoxa zone is constantly 

 submerged beneath ten feet or more of water. At 

 the succeeding spring tides, the same sequence of 

 immature, young and adult animals is obtained by 

 the collector. The absence of mature females and 

 of deposited egg-capsules is not to be explained by 

 a migration of gravid females to some other place 

 more convenient for the purpose of egg-laying ; for, 

 now and again, a solitary capsule may be found during 

 the latest spring tides glued to the weed of the 

 paradoxa zone. By hatching experiments carried 

 out in the laboratory, it may be demonstrated that 

 the time of maturing of the animals coincides with 

 a definite tidal period. It takes either a month 

 or a fortnight for the animals to become mature. 

 They reach maturity at neap-tidal periods. At the 

 beginning of these periods, or soon after, when the 

 zone is submerged continuously for some seven or 

 eight days, C. paradoxa lays its eggs. No matter 

 how the conditions are altered in artificial hatching 

 experiments, C. paradoxa is faithful to its habit: as 

 indicated by the diagram (Fig. 8), which records the 

 results of such experiments, the females lay their 

 eggs only during the neap tides. 



Nor is it without significance that the large 

 yellow-brown eggs of C. paradoxa, rich in food- 

 yolk, hatch with extraordinary rapidity. Within 

 twenty-four to forty-eight hours of the time of lay- 



