SYSTEMATIC 485 



of tlie stomach. These bodies generally appeared when the 

 Tardigrades were kept in the same unchanged water for some 

 weeks. Nothing certain is known as to their nature or origin. 



Systematic. — A good deal of work has recently been done 

 by Mr. James Murray on the Polar Tardigrades and on the 

 Tardigrades of Scotland, many of which have been collected by 

 the staff of the Lake Survey.^ Over forty species have been 

 described from North Britain. 



The following table of Classification is based on that drawn 

 up by Plate : — 



Table of Genera. 



I. The claws of the legs are siinpk^, without a second hook. If tliere are 

 several on the same foot they are alike in structure and size. 



A. The legs are short and broad, each with at least two claws. 



2-4 claws . . Gen. 1. ECHINISOUS, C. ScH. (Fig. 249). 



7-9 claws . . Sub-gen. la. ECHINISCOIDES, Plate. 



B. The legs are long and slender ; each bears only one small claw. 



Gen. 2. LYDELLA, Doy. 



II. The claws of the legs are all or jiartly two- or three-hooked. Frequently 

 they are of different lengths. 



A. There are no processes or jsalps around the mouth. 



I. The muscular sucking pharynx follows closely on the mouth- 

 tube. 

 a. The oral armature consists on each side of a stout tooth 

 and a transversely placed support. 



Gen. 3. MAGROBWTUS, C. Sen. (Fig. 252). 



j3. The oral armature consists on each side of a stylet-like 



tooth without suj)port. Gen. 4. DOYERIA, Plate. 



II. The mouth- tube is separated from the muscular sucking 

 pharynx by a short oesoi)hagus. 



Gen. 5. DIFHASCON, Plate (Fig. 255). 



B. Six short processes or jialps surround the mouth, and two others 



are placed a little farther back. Gen. 6. MILNESIUM, Doy. 



1. Genus ECHINISCUS {^ EUBYDIUM, Doy.). — The 

 dorsal cuticle is thick, and divided into a varying number of shields, 

 wdiich bear thread- or spike-like projections. The anterior end 

 forms a proboscis-like extension of the body. Two red eye-spots. 

 There are many species, and the number has increased so rapidly 

 in the last few years that specialists are talking of splitting up the 



^ Tr. R. Soc. Edinh. xlv., 1908, p. 641. This contains a BibHography of recent 

 literature. See also Richters, Zool. Anz. xxx. , 1906, p. 125, and Heiuis, Zool. Anz. 

 xxxiii., 1908, p. 69. 



