THE FRESH-WATER SHRIMP, OR FRESH-WATER SCREW. 475 



Another strangely formed and closely allied crustacean is the Dactylocera nicceensis, 

 whose habits are, however, very imperfectly known, though it is presumed that they resemble 

 those of the hermit-screw and its kin. In this genus, the head, though large, is not of such 

 enormous comparative dimensions as in Phronima, and is rather squared in form. Some of 

 the strange and grasping legs possess great muscular development, and are armed at their 

 extremities with formidable claws, the movable joint bending over at right angles. 



A small, but very remarkable crustacean, one of the few which really construct a home 

 for themselves, is the CADDIS-SHRIMP, scientifically called Cerapus tabularis. The close 

 resemblance between this creature and the well-known caddis-worm cannot but strike an 

 observer. All the animals belonging to this genus inhabit a case which they are able to carry 

 about with them. In spite of the awkwardness of such an appendage, the Caddis-shrimp 

 passes along at a brisk pace, moving by means of the two pairs of long antennae, which not 

 only look like feet, but are used for locomotion. The real feet are kept within the tube, with 

 the exception of the two front pairs, which are almost wholly used for catching prey and 

 feeding itself. 



Some persons imagine that the tube of this creature is not of home manufacture, but is 

 the deserted residence of some annelid. There is, however, no reason why a crustacean, which 

 is much higher in the scale of creation, should not make as good a tube. The material of 

 which these tubes are made resembles rough leather or papier-mache, and grayish-brown in 

 color, and very tough. They are very small, in some species being not more than the sixteenth 

 of an inch in length, and proportionately small in diameter. Sometimes the tubes are set so 

 thickly upon the plant as to conceal its surface from view. They are set without the least 

 order, and look as if they had been simply flung upon the sea-weed to which they adhere. 

 The common carrageen (Chondus crispus), from which the well-known Irish moss is made, is 

 the plant that is most favored by their presence. When taken out of its cell, the little animal 

 is not unlike a sand-hopper, except that the two pairs of antennae are enormously developed, 

 and the first few pairs of legs are furnished with small claws. 



The generic name Cerapus is taken from the Greek, and is very appropriate, signifying 

 "horn footed." These strange antennae are continually flung forward, grasping at every- 

 thing that comes within their reach, and reminding the observer most forcibly of the peculiar 

 actions of the cirripedes or barnacles. The Caddis-shrimp does not love the very shallow 

 waters, and, except by use of the 

 dredge, cannot be obtained but at the 

 very low tides of March and Sep- 

 tember, those precious days so invalu- 

 able to the practical naturalist, where 

 he finds laid out before him large 

 tracts of the ocean-bed that, except 

 for a few days, at intervals of six 

 months, remain covered with water, 

 and hide their treasures from all eyes. 



The accompanying illustration 

 represents the common FRESH- WATER 

 SHRIMP, or FRESH- WATER SCREW. FRESH-WATER SHRIMP.- Gammam* puiex. (Twice natural size.) 



In common with the other Screws, 



this creature derives its name from its movements when taken from the water and laid upon 

 the ground. Not being able to stand upright upon its feeble legs, it is forced to lie on its 

 side, so that the perpetual kicking of its legs only forces it round in a screw-like fashion, 

 similar to the conduct of the marine screw-shrimp when laid on the sand. 



The Fresh-water Shrimp is extremely plentiful in every stream, and may be seen in great 

 numbers even in the little rivulets that conduct the water from the fields. They lurk in 

 recesses in the bank or under stones that form the bed of the stream, occasionally darting out 

 to seize some prey, and then making their way back again. Occasionally they push them- 

 selves a yard or two up the rivulet, but are sure to come floating back again before very long, 



