INFANCY OF CRABS AND CATERPILLARS 241 



the uncertain care of fate ; but some, like the fresh-water 

 crayfish, carry the eggs about with them attached to their 

 swimmerets, and to these the young cling on hatching. 

 In such cases it is to be noted the " zoea " stage is passed 

 within the egg, so the young emerge in a form not greatly 

 unlike that of the adult. As a rule, when the eggs are 

 thus carried the young hatch in the zoea form and betake 

 themselves off as soon as they leave the egg-shell. 



The motherliness of the crayfish is a matter of ex- 

 pediency. If her young were cast adrift as helpless zoeae, 

 they would be carried down by the stream to the sea and 

 speedily killed. Nature has provided against this catas- 

 trophe by saddling the mother with the care of her young 

 tiU they can safely fend for themselves. In a marine 

 isopod — a near relation of the familiar woodlice of our 

 gardens — Arcturus baffini — the young are always carried, 

 but they are borne on the antennae, which are of huge size ; 

 while in the " opossum-shrimps " the young are carried by 

 the female in a " brood-pouch." In some of the minute 

 and more primitive fresh-water and marine Crustacea a 

 brood-pouch, borne beneath the carapace or shell, instead 

 of by the legs, is commonly met with. In the marine 

 genus Evadne, one of the Cladocera, the young remain in 

 the brood-pouch until they themselves are mature, so that 

 by the time they escape they already bear parthenogenetic 

 embryos in their own brood-pouches ! 



From crabs to caterpillars seems a far cry. Yet both are 

 members of the same great family of " jointed animals," or, 

 as the text-books have it, of the " Arthropoda." Cater- 

 pillars, as everybody knows, are the larval stages of growth 

 of butterflies and moths, and thus, in their transformation 

 from one to the other, they display an even greater con- 

 16 



