SWIMMING ANIMALS 81 



very familiar to those accustomed to rambling along our 

 beaches. They are the so-called " mermaids' purses," little 

 horny capsules with spines or tendrils at the four corners. 

 The smaller, narrower type, with long curling tendrils at its 

 corners, is that of the dog-fish (Scy Ilium), while the large, 

 broad ones with the four spines, belong to the skates 

 (Plate 31). The dog-fish eggs are attached to sea weeds by 

 the parents, who wind the tendrils securely round the stem 

 of the weeds ; these eggs are occasionally to be found on 

 weeds at low tide with the yolk and small developing fish 

 inside, because the " mermaid's purse " is of course merely 

 the case in which the egg lies. The skate's eggs, on the 

 other hand, are deposited in deeper water, where they are 

 buried in the sand with the two spines projecting above the 

 surface, and through these a current of water is drawn into 

 the case by the developing fish for breathing purposes. 

 These eggs of the dog-fishes and skates take many months 

 to hatch, although most other fishes hatch out within about 

 a fortnight after the eggs are laid. 



One of the most surprising cases of spawning instinct is 

 exhibited by a little fish that abounds on the shores of 

 California. This fish, the Grunion (Leuresthes tenuis), 

 belonging to the Atherine family, deposits its eggs in the 

 sand at the high-tide mark along the sandy beaches. This 

 it does one to three days after the highest spring tide, 

 burying the eggs two or three inches beneath the surface 

 of the sand. Here the eggs remain and develop, until in a 

 fortnight's time, when the high tides once more cover them, 

 they are ready to hatch. Now notice the providence of 

 nature. If those eggs had not been laid just after the 

 highest spring tide there is quite a possibility that the next 

 high spring tide a fortnight later, might not have been quite 

 so high, thus preventing the eggs from being reached by the 

 water ; and in this case, being ready to hatch, they could 



