337 
velopment. Secondary sexual differences have been discovered in 
the posterior legs of sorae species of Pauropodidæ and will be dealt 
with under this family; if similar or other sexual differences exist 
in inembeis of the two other families I do not know, my material 
of thern being very small. 
Every one who has seen living specimens of the family Pau¬ 
ropodidæ has certainly observed, that the animals are able to elon- 
gate their body or to shorten it by contraction in a very high de- 
gree. The length in proportion to breadth therefore differs much in 
specimens preserved in spirit, and the value of these dimensions is 
rather limited; animals collected in strong alcohol are generally 
much contracted and besides difficult to examine. The length of the 
segments is of slight value, and I always compare the length of the 
set® with the length of the eyes or with the breadth of the seg¬ 
ments, this dimension being less varying than the length and more 
easy to measure with certainty. 
Many and for the most part new characters have been made 
use of in the following descriptions. Nevertheless I have not utili- 
zed all differences, having discarded some which are difficult to ob- 
serve without apparently being very valuable, and others which are 
rather insignificant. The lower side of the head has been left out 
of considciation: the extent of the eyes and the hairs present diffe¬ 
rences which are difficult to describe and require a set of rather 
laige figuies. The two pairs of setæ on the first sternum are not 
mentioned; they present difference in shape and relative length, and 
a future student will perhaps figure them, though the value must 
be rather slight. — A leg of the first or the second pair could 
be figured with the same enlargement as the ninth pair, in 
order to elucidate the differences between the length etc. of the 
two pairs, but for the distinction between rather closely allied spe¬ 
cies these differences will avail almost nothing. In the family 
Pauropodidæ the hairs on the terga of the trunk are passed by 
vitli exception of those on the last or on the two posterior seg¬ 
ments; on this topic a few remarks are found below. 
Vidensk. Medd. fra den naturh. Foren. 1901. 
22 
