TARDIGRADA 85 



manni (43), has nine segments. What they mean by segments can only be 

 ascertained by studying the figures which these writers have given. Richters' 

 scheme is perhaps the most useful. It does not aim at accounting for all the 

 morphological segments of some hypothetical primitive or typical Tardigrade, but is 

 merely a division of the body for practical use to systematic naturalists. 



He reckons six segments, and indicates them by roman numbers, I. to VI. These 

 numbers are here adopted to distinguish the segments, and as there are two distinct 

 types of segmentation I give two figures, one of each type, on which the segments 

 are numbered, and other points of structure indicated (see Plates XVIII. Fig. 34, 

 and XVI. Fig. 14). 



In one group of Echinisci the segments V. and VI. have coalesced so completely 

 that there is no external mark of their separation (Plate XVI. Fig 14). This 

 includes the great majority of the species. Segment I. is the head, II., III., and IV. 

 the body segments bearing the first, second, and third pairs of legs, V. -f VI. bears 

 the fourth legs. The reckoning of V. as a segment is rather inconvenient, as there 

 is in most species no visible trace of it. 



In the other group, which includes only about a dozen species, segments V. 

 and VI. remain distinct (Plate XVIII. Fig. 34). When V. is separate it usually 

 bears a pair of plates, like those of segments III. and IV., but it may be a half-ring, 

 without trace of division in the middle, as in E. pulclier here figured. 



All of the plates are liable in one species or another to be subdivided in various 

 ways. This usually only affects the surface markings. The divisions may be merely lines 

 separating different areas, or they may be broad bands devoid of markings. The median 

 plates are often divided by a transverse line into two parts (E. novcezeelandice, Plate 

 XV. Fig. 5), or by median lines into pairs (E. pulcher, Plate XVIII. Fig. 34). 



E. tessellatus (Plate XVI. Fig. 15) is an extreme case of the division of segments 

 II. and V. + VI. by transverse and longitudinal bands. E. scrofa, Richters (26), 

 is an example of subdivision of the median plates into many narrow bands. 



The plates of the first and second pairs are commonly divided into two parts by a 

 transverse plain band (E. duboisi, Plate XVII. Fig. 19, E. spinulosus, Plate XIX. 

 Fig. 38). This band occupies a furrow. Sometimes the separation is a mere line, 

 and the markings continue into the furrow. Occasionally there are two lines on each 

 plate, separating narrow portions at the anterior and posterior borders, without any 

 cessation of the markings (E. tessellatus, Plate XVI. Fig. 15). 



The markings of the plates are of several kinds. As their true character is often 

 in doubt they are named from their appearances. There are pellucid dots which do not 

 appear to project from the general surface, actual projecting granules (E. granulatus, 

 .Doyere, very large in E. tessellatus, Plate XVI. Fig. 15), pits or apparent perfora- 

 tions, and reticulation of raised lines. The reticulation may be simply the borders of 

 adjacent depressions (E. intermedius, Plate XVI. Fig. 17). Very peculiar are the 

 close-set spicules of E. spiculifer, Schaudinn (41), and the reticulation of pearly dots 



