THE CRUSTACEANS 111 
are especially abundant upon the beaches at the times of the spring 
tides. The eggs hatch in about a month, and the young bear a re- 
markable resemblance to the trilobites so that they are said to be 
in the trilobite stage. The sharp terminal spine develops later, 
after moulting. 
Horseshoe crabs have been used for making fertilizer in Dela- 
ware Bay and are nearly exterminated in that region. ‘They are 
among the most interesting of all marine animals, and are probably 
the last survivors of a race which may have been a connecting link 
between the trilobites, crustaceans, and scorpions. ‘There are very 
few existing species, one being found on our coast and several on 
the coast of Asia. 
THE SEA SPIDERS 
Pycnogonide. 
These are generally small creatures which crawl slowly over 
hydroids and sea weeds, and bear a superficial resemblance to 
spiders. Their true relationships are, however, a puzzle to 
naturalists. 
The body is extremely small, so that the stomach aud _ re- 
productive organs extend outward into the long, stout legs, the 
stomach in some species reaching even to the tips, while the repro- 
ductive organs open on the lower sides of the second joints. 
There are typically seven pairs of appendages in the male and 
six in the female, the third pair being absent in the females of 
many species. In the male, however, these are developed into egg- 
carrying organs, for he gathers the eggs into balls as soon as they 
are laid, and fastens them to his third pair of legs by means of a 
cement which issues from openings at the fourth joints of his walk- 
ing legs. When the young hatch they often crawl over the male 
in considerable numbers. In other genera the young enter the 
digestive cavities of hydroids, and form gall-like enlargements upon 
the stems, within which they live. 
Phoxichilidium maxillare is a small species which varies in 
color from blackish-brown through sepia to almost white, and 
spreads about one inch. It is commonly found crawling over 
hydroids and sea-squirts, on shelly bottoms. The young live for a° 
