2 20 Animal Life and Intelligence. 



metrically from above downwards. It lays, perhaps, eighty 

 to a hundred eggs. Each of these is large, and has a 

 rich supply of nutritive food-yolk. Each is also protected 

 by a horny case with pointed corners — the so-called sea- 

 purse of seaside visitors. These are committed by the 

 skate to the deep, and are not further cared for. But the 

 abundant supply of food-yolk gives the little skate which 

 emerges a good start in life. On the other hand, the 

 turbot, one of the bony fishes, flattened from side to side 

 with an asymmetrical head, lays several millions of eggs, 

 which float freely in the open sea. These are minute and 

 glassy, and not more than one-thirtieth of an inch in 

 diameter. When the fishes are hatched, they are not 

 more than about one-fifth of an inch in length. The 

 slender stock of food-yolk is soon used up, and henceforth 

 the little turbot (at present more like a stump-nosed eel 

 than a turbot) has to get its own living. Hundreds of 

 thousands of them are eaten by other fishes. 



Or, if we compare such different vertebrates as a frog, a 

 sparrow, and a mouse, we find that the frog produces a 

 considerable number of fertilized ova, though few in com- 

 parison with the turbot, each provided with a small store 

 of food-yolk. The tiny tadpoles very soon have to obtain 

 their own food and run all the risks of destruction. Few 

 survive. The sparrow lays a few eggs; but each is 

 supplied with a large store of food-yolk, sufficient to meet 

 its developmental needs until, under the fostering influence 

 of maternal warmth, it is hatched. Even on emerging 

 from the eggs, the callow fledglings enjoy for a while 

 parental protection and fosterage, and, when sent forth 

 into the world, are very fairly equipped for life's struggle. 

 The mouse produces minute eggs with little or no food- 

 yolk ; but they undergo development within the womb of 

 the mother, and are supplied with nutrient fluids elaborated 

 within the maternal organism. Even when born, they are 

 cherished for a while and supplied with food-milk by the 

 mother. 



The higher stages of this process involve a mental 



