transverse plates attached at their forward edges. 

 Each of these plates protects a pair of gill books, of 

 which the individual "leaves" are the respiratory 

 organs. When a horseshoe crab swims, it flaps the 

 plates with the gills and jerks the legs in a rhythm 

 that propels the body along like an animated wash 

 basin. 



In springtime the horseshoe crabs migrate to shal- 

 low water, and the males hunt out the larger females. 

 Sometimes a "cow" crab is seen pulling a chain of 

 four or five males, each clipped to the rear of the one 

 ahead. When her eggs are ready, the cow crab drags 

 her escort on shore at some sandy spot while the tide 

 is at its peak, and there burrows into the beach to 

 lay. Weeks later, and long after the parents have sep- 

 arated and returned to deeper water, the young crabs 

 emerge from the sand. They have virtually no tail 

 and bear a superficial resemblance to the extinct tri- 

 lobites; so the larva has come to be known as the 

 "trilobite stage" of development. Soon it transforms 

 into a diminutive horseshoe crab. 



At intervals each growing animal gets too cramped 

 in its shell and sheds it, molting to a larger size. Un- 

 like other arthropods, however, the line of weakness 

 which breaks and liberates the horseshoe crab does 

 not run down the midline of its back. Instead, a 

 horseshoe crab splits along the forward rim of its car- 

 apace and creeps out, as though escaping from its 

 own mouth. The cast shell is left seemingly intact, 

 and waves often cast it ashore where a beachcomber 

 can pick it up. 



Young and comparatively soft-bodied horseshoe 

 crabs fall prey to true crabs, fish, and many birds, 

 including particularly gulls. Those that survive be- 

 come comparatively immune to attack. Eels often 

 follow horseshoe crabs into the breeding shallows 

 and gulp in the eggs as fast as they are extruded. 

 Coastal Indians used to eat horseshoe crabs, and ac- 

 cording to Thomas Hariot they were "good food." In 

 more recent times, coastal fishermen have built traps 

 to capture horseshoe crabs for use either as cheap 

 nourishment for pigs and chickens or to be dried and 

 ground as fertilizer. 



The horseshoe crab encountered by Sir Walter Ra- 

 leigh's expedition was Limidiis polypheinus. Today 

 it is known from the Bay of Fundy all along the At- 

 lantic coast to Key West, and at a scattering of places 

 in the Gulf of Mexico as far as Yucatan. Formerly it 

 may have been present in the West Indies, for old 

 books on the natural history of Jamaica include il- 

 lustrations of this animal. 



Counterparts of Linuiliis occur in the Orient: Car- 

 cinoscorpius and Tachypleits along the coasts of 

 China, Japan, the East Indies, and one species as far 

 as India in one direction, the Philippines in the other. 

 Carcinoscorpiiis readily invades brackish shallows, 

 and has been found in the Hugh River at Calcutta, 



ninety miles from the open sea, in water that is prac- 

 tically fresh. 



The Spiders and 



1 heir JVIU {Class Arachmda) 



In Greek mythology, Arachne was a Lydian girl 

 who grew so proud of her ability as a weaver that 

 she challenged the goddess Athena to a contest. For 

 this impertinence Athena changed Arachne into a 

 spider and condemned her to weave forever with silk 

 from her own body. 



Most members of the class Arachnida are indeed 

 skilled weavers, and the silk they produce is one of 

 the most marvelously versatile materials in all nature. 

 But with some 29,000 diflferent kinds of arachnids 

 known, wide variation is to be expected. This is the 

 second most varied class of animals, exceeded only 

 by the insects. 



SPIDERS 



Spiders (order Araneae) are constricted conspic- 

 uously between a cephalothorax and an unsegmented 

 abdomen. Their webs can be found almost anywhere 

 on land. Charles Darwin reported them near the 

 Equator in mid-Atlantic on the remote, isolated, 

 guano-covered cluster of rocks known as St. Paul's 

 Island — halfway between the bulge of Africa and the 

 bulge of South America. The British expert on spi- 

 ders. Dr. Thomas H. Savory, recorded jumping spi- 

 ders trailing silken threads at 22,000 feet above sea 

 level on Mount Everest, a good 4000 feet above the 

 highest plant and with no other animal life for com- 

 pany. He concluded that cannibalism was their only 

 way of existence, and in this they had to depend upon 

 a continuous immigration of more spiderlets, riding 

 the mountain winds on balloons and parachutes of 

 self-made silk. 



Wherever a spider travels, whether by running or 

 leaping, it ordinarily spins out a fine strand of silk on 

 which it can go back in an emergency. In addition, 

 most spiders produce webs of some kind. 



Early in the 1800's, the French entomologist P. A. 

 Latreille classified the webs of spiders into four main 

 groups: those of circular form suspended in a verti- 

 cal plane, such as the familiar orb web of the garden 

 spider; those with supporting strands in all directions, 

 such as the house spider weaves in window corners, 

 or with a horizontal sheet of web among bushes or on 

 the ground, such as the work of the doily spiders; 

 those of funnel shape, expanding from some crevice 

 or natural hole in which the spider waits for prey to 

 pass; and tubular webs spun in a hole dug by the 



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