TARDIGRADA 87 



plates. Sometimes the dorsal processes are nearer the median line (E. borecdis, &c.), 

 and when there are any processes on segment V. they are usually near the middle 

 line (E. islandicus, E. novcezeelandice). 



In the group which has segments V. and VI. united there are usually only two 

 median plates. A well-defined third median is rare, but there is often an area in 

 the triangular space behind the second pair, dotted exactly like the plates, but 

 without definite bounding lines. 



In the group which has V. and VI. separate there are always three median plates, 

 although they are often very obscurely separated from the pairs in front of them. 



In the majority of species there is a serrate fold of skin on the fourth leg. The 

 teeth or spines on this fold vary from short and blunt to slender and acute, and are 

 useful for distinguishing species. 



Near the base of the fourth leg, on the outer side, there is usually a blunt palp. 

 On the first leg there is often a longer or shorter sharp spine. Rarely there are 

 little spines on other legs (E. perarmatus). 



The colour of Echiniscus is usually red, varying from pale pink to deep crimson or 

 scarlet. A very few species are yellow (E. mutabilis, sylvanus, tessellatus), green 

 (E. viridis) or colourless (E. intermedius). 



The eggs are always smooth, shortly oval, and are laid in the cast skin. From 

 one to nine have been seen in a single skin. As many as nine is quite exceptional, 

 the usual number being three or four. 



Oreella. Like Echiniscus in every important detail of structure except that the 

 body is not covered with plates. It is soft and flexible like Macrobiotus. The only 

 trifling differences from Echiniscus are that the " Auricle " at the base of seta a is 

 elongate and acute, and is elevated on a large papilla which bears the seta also ; 

 and that the anterior cirri at the mouth are replaced by narrowly conical processes. 



The generic forms of land Tardigrada do not seem to be very numerous. 

 Although work has been done in all regions of the globe now, no new genus has 

 been found since Diphascon (Plate, 1888) till now. 



Oreella has no eye-spots. The eggs are unknown. 



Milnesium. Though several species have been described, their differences are 

 slight and inconstant, and only M. tardigradum is here admitted. It is a large 

 animal with very wide gullet and elongate pear-shaped pharynx, in which there are 

 no rods such as Macrobiotus has. There are six cylindrical palps round the mouth, 

 and a pair farther back. A distinct genus, Acrophanes, of no value, was separated 

 by Ehrenberg (5) apparently to receive a shrivelled skin of Milnesium. 



The claws are very different from those of Macrobiotus. On each foot there are 

 two claws, usually with two or three, or even four, branches. The three-branched claw 

 appears to be homologous with a pair of Macrobiotus claws, including the supple- 

 mentary point. On each foot there are also two very slender, bristle-like claws, each 

 with a very fine supplementary point. 



