THE JOINTED-FOOT ANIMALS 



155 



worms. Sometimes they plow a few inches below the sur- 

 face. The older ones, thirty to forty centimeters in length 

 (twelve to sixteen inches), burrow in deeper water; small 

 ones may often be seen on sand-flats where the water is 

 only a few inches deep. At the time of high tides in May, 

 June, and July, the mature males and females, the latter 

 always the larger, leave the water and make their way up 

 the sandy shore to a point just below high-water mark. The 

 female digs a hole in the sand, deposits her eggs, and the 

 male follows and deposits the " milt," or spermatozoa, over 

 the eggs. Both animals then return to the deeper water, 

 and the retreating tide covers the eggs with sand. The young 



Of, 



FIG. 81. Horseshoe Crab 



hatch in about four or five weeks, and make their way into 

 shallow water. When first hatched they resemble young 

 trilobites in form. 



The horseshoe crab is a peculiar type. It shows many 

 points of similarity to both crustaceans and arachnids, par- 

 ticularly the scorpions, and it may be that the latter have 

 descended from these aquatic forms, which are an extremely 

 ancient stock. Some of the fossil allies of the horseshoe crab 

 grew to be five or six feet long. 



