150 NATURAL HISTORY OF AQUATIC INSECTS CH. 



The spawn of the Angler Fish (Lophius) spreads out 

 on the surface of the sea as a sheet, eight to ten feet 

 square. The Perch discharges her eggs enveloped in 

 a transparent substance, which she rubs off against 

 stones. They form a mass of loosely interwoven 

 strings, several feet long. The female Ceratodus also 

 lays her eggs in long, gelatinous strings. 



Lastly, the Frog furnishes the most familiar ex- 

 ample of a transparent egg-mass. Laid in stagnant 

 water, the Frog-spawn does not require to be moored. 

 The eggs are so slippery that Insects or Birds, ex- 

 cepting only the broad-billed Duck, cannot, grasp 

 them. They are spaced so that each gets its fair 

 share of sunlight and air. Then the slimy covering 

 detains bubbles of air which expand in the w r armth of 

 the sun's rays, and buoy up the eggs. Frogs' eggs, 

 when fresh-laid and free from bubbles, are slightly 

 heavier than water, and sink. After no long time 

 they float at the surface, except when the weather is 

 unusually colu. The presence of antiseptic proper- 

 ties in Frog-spawn is attested by the persistence of 

 the empty egg-envelopes for weeks after the Tadpoles 

 have hatched out. In the end they often become 

 overgrown by green cells, and in that condition are 

 eaten by the Tadpoles. The spawn of the Toad 

 forms long ropes. This is probably a provision for 

 hatching in slow streams. The eggs of the Frog 

 might possibly be carried away in such places, but 

 the egg-ropes of the Toad, which are many yards 

 long, get entangled in weeds, and never float far. 



The egg-ropes of Chironomus are well worth the 

 attention of the naturalist for another reason, viz : 



