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



common medusae. It will occasionally leave this curious residence, and return to it at 

 will. It is about half an inch in length, has the two first pairs of feet shortest, tipped with 

 a claw, and has the three last pairs of legs longer than the others. The name of this 

 crustacean is Metoecus medusarum. Mr. Spence Bate separates all these parasitic 

 animals into a distinct family, under the name of Phronimadae. All the members of 

 this family have the mandibles very large, some of the legs prehensile and oddly formed, 

 and the head of enormous comparative size. Some of them attach themselves to fishes, 

 and others to medusae. 



FIGS. C and D represent another strangely formed and closely allied crustacean, 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. 

 The strange and grasping legs may be seen by reference to the illustration, some of 

 those members possessing great muscular development, and being armed at their 

 extremities with formidable claws, the moveable joint bending over at right angle. 



FIGS. E and F represent a small, but very remarkable crustacean, one of the few which 

 really construct a home for themselves. The close resemblance between this creature 

 and the well-known caddis-worm cannot but strike an observer. All the animals belong- 

 ing 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 crusta- 

 cean, 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, signify- 

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

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

 the peculiar actions of the cirrhipeds 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 September, those precious days so invaluable 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 central upper figure in the next illustration represents the common FRESH-WATER 

 SHRIMP, or FRESH-WATER SCREW. 



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 fields. They lurk 



