LIMITATION OF FAMILIES 121 



under the shell on the back, and in some cases are fed by a nutritive 

 juice which reaches them from a large blood-space. In many others, 

 the eggs are carried in pouches attached to the body of the parent, 

 or are suspended to her legs. In all these small flea-like crustaceans, 

 however, the development is indirect, and at least some meta- 

 morphoses are gone through. In the sandhoppers and slaters the 

 numbers of the young are still further reduced, and the embryos, 

 carried by the mothers in brood-pouches, are fed and protected 

 until they have almost completely attained the adult structure. 

 In the higher crustaceans, such as shrimps and prawns, crabs, 

 lobsters and crayfishes, the eggs are rather numerous, and are 

 cemented to the under surface of the body of the mother, forming 

 the familiar " berries " which in prawns, crabs and lobsters turn 

 red on boiling. In those that live in the sea, when the eggs hatch, 

 the larvae leave the mother and have to fend for themselves. In 

 the fresh-water forms, however, such as the familiar crayfish, the 

 eggs are much larger in proportion to the size of the animals, and 

 are much less numerous. The complete development takes place 

 before hatching, whilst the egg is still carried by the mother, and 

 when the young creature emerges it is almost a perfect miniature 

 of the parent. It enjoys the protection of the mother for a stiU 

 longer period, clinging to her with its pincers. 



Scorpions and spiders are terrestrial, air-breathing creatures of 

 high organisation, and show many instances of elaborate precautions 

 for the care of the young, and of a resulting reduction in the numbers 

 of the brood. Scorpions are the larger, more powerful and better 

 armed, and in them the process has gone furthest. The eggs are 

 hatched inside the body of the mother, and each brood consists of 

 no more than about a dozen individuals, which are born two at a 

 time. From their first appearance they can be recognised as little 

 scorpions, differing only in size, in paler colour and in a few minor 

 details from their parents. They at once find their way to the back 

 of the mother, and the whole family is carried in this way for some 

 weeks, until the young creatures have gone through several moults 

 and become large enough and strong enough to look after themselves. 

 During this time they enjoy protection, for a scorpion is a formidable 

 creature with few enemies sufficiently daring to attack it. The 

 young feed on scraps of the spiders, cockroaches and other insects 

 which the mother catches and slowly picks to pieces. 



Spiders are far from having reached the economy of breeding 

 habits shown by scorpions. The young are always hatched outside 



