186 J. MURRAY ON WATER-BEARS, OR TARDIGRADA. 



thick spines, E. imherhis is further modified ; the four cirri 

 and palps near the mouth are lacking, so that there only remaibi 

 process a and its palp, characteristic of all known Echinisci. 



In related genera further modifications take place. In three 

 genera all the processes on the head are reduced to small palps 

 or spicules, Milnesiimi has all six processes near the mouth 

 as palps, and has another pair of similar palps corresponding to 

 a of EchinisGus. Echiniscoldes has only one pair of spicules at 

 the mouth, and a pair at each side in the position of a. 

 Tetrakentron has three small palps near the mouth, one of them 

 medium, and a spicule and palp recognisable as a and its palp. 



The genera with well-developed cirri are variously modified. 

 Microlyda has a and its palp normal, the palps, however, 

 relatively large, and only one pair of forked cirri near the 

 mouth. UalechiniscK'S, Batlllipes and Oreella have very similar 

 cirri, all six being present ; the palp at the base of a is greatly 

 enlarged and elongate, and is borne, with a, on the summit of 

 a more or less elevated process. The palp is largest in Batillipes. 

 The palps near the mouth are lacking in Haleckbiiscus and 

 Batillipes, and are reduced to very small points in Oreella. 



Processes on the body. It is not every Echiniscus which has 

 processes (spines, setae or knobs) on the body, nor are these 

 processes confined to this genus, still paired processes are 

 eminently characteristic of the great majority of the species. 

 The commonest processes are certain lateral ones, which Richters 

 distinguishes as h, c, d and e, and certain dorsal ones over 

 c and d. 



Ttie only genera in which there are no body processes are 

 Oreella, Miliiesiu7n and Diphascon. All the marine genera, 

 Echlniscoides, Microlyda, Batillipes, Halechiniscus and Tetra- 

 kentron, have some of the lateral processes corresponding to. 

 c, d, e ', e being the most constantly present. 



Species of Maci^ohiotus have the body usually smooth, without 

 processes, rarely papillose. Some half-dozen species have pro- 

 cesses, usually small spines or blunt knobs ; in M. ornatus long 

 spines. Though these processes are paired, they are so numerous 

 in M. ornatus, M. j^cipillif^'^ ^nd M. sattleri that it is hopeless 

 to regard them as homologous with b, c, d, e of Echiniscus (in 

 M. polychaetus the whole body is covered with spines which do 

 not appear to be paired.) , 



