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



to EchinisGus than any of the marine genera, while yet approach- 

 ing Macrobiotics in the possession of bearers and an unarmoured 

 skin. 



Baiillipes, in view of its possession of five toes, in an order in 

 which four is almost universal, must be regarded as the most 

 aberrant of the Echiniscoid genera. Eccentricities of this kind 

 are uncommon in nature. When any structures exist in a 

 definite number throughout an order, there is rarely any 

 variation in the number except in the direction of reduction or 

 duplication. 



Echiniscoides also departs from the normal number of toes, 

 but in a direction more readily understood, since there is still 

 a tendency to have an even number (8), double that normal in 

 the order. 



Microlyda {Lydella) has the claws reduced to one on each foot. 

 While it is not difficult to derive such a form as this from the 

 normal type, it has been plausibly suggested that Microlyda is a 

 larval form and that the adult might have an even number of 

 claws (two or four). 



Macrohiotus is also an extensive genus of water-bears. It even 

 exceeds Echiniscus in the number of species contained in it. It 

 is, however, a much less homogeneous genus than Echiniscus ; it 

 contains large groups of very diverse structure, and will probably 

 have to be broken up even more completely than Echiniscus, 



Remote though Macrohiotus is from Echiniscus, there are not 

 wanting signs of affinity, in the rare occurrence among Echinisci 

 of bearers, and even of chitinous rods in the pharynx ; also in the 

 possession by some Macrohioti of processes probably homologous 

 with those of Echinisci. 



Diphascon stands so near Macrohiotus that it has often been 

 doubted whether it could be maintained. The sole constant 

 character is the elongated and flexible gullet, and that is reduced 

 to a minimum in D. angustatuni, and, moreover, the gullet may 

 be exceptionally elongated in a true Macrohiotus. There are two 

 subsidiary characters which confirm my belief in the validity of 

 the genus there is a definite type of claw, and many specie* 

 have a very narrow pharynx. 



The Diphascon claw is not confined to the genus several 

 Macrohioti have it but its constant association with the flexible 

 gullet shows that these characters indicate a natural group. 



