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present often excellent characters. (On the tactile setæ in imma- 
ture specimens sorne remarks are set fortli belovv). 
Anal begment. It lias been much neglected by all authors, 
and yet it piesents rnany excellent specific characters. Its tergum 
seems sometimes to be longer, sometimes shorter than its sternum, 
but this dillerence is often, but not alvvays, casual and depends 
upon the laet, that one of the two plates is more withdrawn into 
the preceding segment or pushed more backward than the otlier. 
Sometimes this goes so far that the posterior part of the sternum 
not only covers the end of the segment, but has been bent upward 
and forward, occupying the hindmost part of the dorsal surface (pi. 
\ , tig. 1 b); sometimes the tergum shows a similar curvature, occu¬ 
pying the hindmost part of the ventral surface (pi. III, tig. 2 e). 
Sometimes specimens of the same species present considerable ca¬ 
sual difference in the structure mentioned (comp. fig. 2 d on pi. III 
with fig. 2 e), and it bewilders the student in the beginning. — 
Ihe tergum has always in all three families three pairs of setæ 
which I name: the submedian (a 1 ), the intermediate (a 2 ) and the 
lateral pair ( a 3 ); their relative length in proportion to each other 
and to the breadth of the segment and their arrangement present 
good characters; besides the tergum has at the hind margin or on 
the ventral side a singular pair of setæ, the styli(s), which differ 
exceedingly in length and shape in various species. (In one species, 
Pauropus argentinensis, I have still discovered close above the styli 
a pair of setæ which are so short that in this rather large species 
they could only be observed under high magnifying power; I can 
not interpret their absence in other species, and perhaps they are 
sometimes present, but so rudimentary that I have been unable to 
detect them. — In specimens with only eight pairs of legs I found 
a pair of short setæ (d) rather near the base of the lateral margin, 
and these setæ are always absent in the adults). — The sternum 
possesses one, two or three pairs of setæ; these I name the poste¬ 
rior (b 1 ), the lateral (b 2 ) and the anterior (6 3 ) pair ; the posterior 
pair, which is inserted on the hind margin, is always well de ve- 
