240 THE INFANCY OF ANIMALS 



yet appeared — they are not developed till the final, adult 

 form is assumed. 



How strange and varied are the zoea stages of the 

 Crustacea will be brought home still more forcibly, after a 

 glance at the zoea of a near relation of Penceus — the ser- 

 gestes. This, as our illustration shows, presents a most 

 extraordinary appearance, owing to the excessive develop- 

 ment of spines. This formidable armature probably 

 affords protection against enemies, but it seems more 

 particularly to serve to increase the surface of the body 

 and so retard sinking, as the sergestes larvae, like other 

 very spiny larvae, live at the surface of the sea. The 

 nauplius larva of one of the barnacles, and the zoea of 

 the common porcelain crab (Porcellana longicornis), afford 

 other illustrations of this excessive development of spines, 

 to serve the same end. 



But as if to show her resourcefulness, her love of success- 

 ful experiments. Nature is always displaying contrary 

 means of attaining the same end. Hence, having as it 

 were demonstrated the need of spines as aids to delicate 

 creatures of limited muscular power, but which can only 

 keep afloat by constant effort, she proceeds to display 

 zoeae of a totally different type, such as that of the spiny 

 lobster (Palinurus vulgaris). In its adult state this creature, 

 which spends its days crawling at the bottom of the sea, 

 is as spiny as a hedgehog. Yet in its early, surface- 

 swimming days, spines have no place. Instead, the body 

 is excessively flattened, till it is no thicker than a sheet of 

 paper, and as translucent as glass — hence these little 

 creatures are also known as " Glass Crabs." 



To those who would ask the question, " Are crabs good 

 mothers ? " we would answer — using the term crab in a 

 wide sense — Some are. The majority leave their eggs to 



