122 THE STORY OF FISH LIFE. 



This is well seen amongst the invertebrates. 

 With the vertebrates changes of this kind also 

 occur, but not on quite so marked a scale. As 

 Prof. Miall has aptly put it, the choice between 

 embryonic or larval development depends "upon 

 the number of the family and the capital at 

 command. These are animals which are like 

 well-to-do people who provide their -children 

 with food, clothes, schooling and pocket-money. 

 Their fortunate ofF-spring grow at ease, and are 

 not driven to premature exercise of their limbs 

 or wits. Others are like starving families, 

 which send the children, long before their 

 growth is completed, to hawk matches or news- 

 papers in the streets." 



The young fish then, being the product of a 

 small egg, ill- provided with nutritive yolk, comes 

 into the world in a larval condition. The precise 

 form of larva may be described as the tadpole- 

 larva, and it is interesting to note that this form 

 is common to larvae lower in the scale than the 

 fishes — to wit, those remarkable creatures which 

 lie in the borderland between the vertebrate and 

 invertebrate — the ascidians or sea-squirt?; and 

 the larvae higher in the scale, the amphibia, such 

 as the frog and toad or the newt, for example. 

 The tadpole in its simplest form is a long-tailed 

 animal strengthened by a kind of fibrous rod 

 running down its body from the head to the tail, 

 immediately below the spinal cord. It breathes 

 by gills, and has a mouth in the form of a suck- 

 ing disc. "It is a cheap form of larva," says 

 Prof. Miall, "whenreiuced to its lowest terms, 

 requiring neither hard skeleton, nor limbs, nor 



