476 



THE SKELETON-SCREW, OR MANTIS-SHRIMP. 



allowing themselves to be passively swept along by the force of the water as if they were dead, 

 but starting suddenly into active exertion as soon as they reach their former haunts. 



In the water this crustacean moves by a series of jerks, and mostly lies on its side, though 

 it often swims with its back uppermost, and frequently rotates as it passes along. It is a 

 voracious creature, feeding upon dead fishes or any similar carrion. It is fond of the muddy 

 parts of the stream, liking to conceal itself in the soft alluvium when fearful of danger. The 

 eggs of the female are kept for some time under the abdomen, and the young remain in that 

 situation until they have attained sufficient strength to shift for themselves. 



Three other species are marine. These are the Wood-boring Shrimp, the Skeleton-screw, 

 and the Whale-louse. The WOOD-BORING SHRIMP is a crustacean that nearly rivals the ship- 

 worm itself in its destructive powers. It makes burrows into the wood, wherein it can conceal 

 itself, and at the same time feast upon the fragments, as is proved by the presence of woody 

 dust within its interior. Its tunnels are made in an oblique direction, not very deeply sunk 

 below the surface, so that after a while the action of the waves washes away the thin shell 

 and leaves a number of grooves on the. surface. Below these, again, the creature bores a fresh 

 set of tunnels, which in their turn are washed away, so that the timber is soon destroyed in 

 successive grooved flakes. 



According to Mr. Allman, its habits can be very easily -watched, as if it is merely placed 

 in a tumbler of sea-water, together with a piece of wood, it will forthwith proceed to work and 

 gnaw its way into the wood. 



In this creature the jaw-feet are furnished with imperfect claws, and the tenth segment 

 from the head is curiously prolonged into a large and long spine. The great flattened append- 

 ages near the tail seem to be merely used for the purpose of cleaning its burrow of wood dust 

 which is not required for food. The creature always swims on its back, and when com- 

 mencing its work of destruction, clings to the wood with the legs that proceed from the 

 thorax. The Wood-boring Shrimp is one of the jumpers, and, like the sand-hopper, can leap 

 to a considerable height when placed on dry land. 



Another wood-boring shrimp will be described in a succeeding page. 

 In the illustration is seen the marine Crustacea called appropriately the SKELETON- 

 SCREW, or MANTIS-SHRIMP. The bodies of the Skeleton-screws 

 are indeed skeleton-like in. their bony lankness, but their appe- 

 tites are by no means small in proportion to their size. They are 

 furnished with terrible instruments of prehension, their first and 

 second pairs of legs being devoted wholly to this purpose. The 

 last joint but one is enormously large, and the last joint is thin, 

 and shuts down like the blade of a claspknife into its haft, the 

 groove being represented by a double row of spines between which 

 the blade is receive'd. The blade itself is finely notched along the 

 edge. These claw-like terminations to the legs are used not only 

 for seizing prey, but for grasping the branches and drawing the 

 long attenuated body from one part to another. 



Mr. Gosse, who has paid much attention to these curious 

 beings, remarks that their movements among the marine vegeta- 

 tion are wonderfully like those of the spider monkeys among the 

 branches, their long thin bodies adding to the resemblance. They 

 run about with great agility, and are always to be found in 

 the branches of the Plumatella cristata. The same writer has given a very interesting history 

 of the Mantis-shrimp : 



" Their manners are excessively amusing. The middle part of their long body is destitute 

 of limbs, having instead of legs two pairs of oval clear vesicles, but the hinder extremity is 

 furnished with three pairs of legs armed with spines, and a terminal hooked blade like that 

 already described. With these hindermost legs the animal takes a firm grasp of the twigs of 

 the polypidom, and rears up into the free water its gaunt skeleton of a body, stretching wide 

 its scythe-like arms, with which it keeps up a see-saw motion, swaying its whole body to and 



MANTIS-811R1MP.- Caprella Unearte. 



