BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND. 5. N:0o 18. 13 
a difference between the genera that have clasping and svim- 
ming-feet on the first thoracic segment, and that the clasping- 
foot is a transformation of the swimming-foot. Second pair 
of feet (P1. IV. Fig. 5.) consisting of one undivided basal 
piece and two branches not separated from it by any joint; the 
inner rudimentary, with a single seta at the apex, the outer 
having two longer sete at the apex and three spines on the 
outer margin. Other pairs of feet wanting. 
The body of the young in the second stage is six-jointed. Furca 
with only one seta at the apex, and having now assumed the same 
appearance that it has in the full-grown animal, the outer seta, 
belonging to the preceding stage, having disappeared. Anterior 
antenne six-joimnted, with two basal joints of equal length and 
four terminal ones. Posterior antenne having three geni- 
culate sete and differing from those of the full-grown ani- 
mal by having only three spines at the outer margin. Se- 
condary branch slender and having almost its final appea- 
rance. The branches of the first pair of feet, now two-join- 
ted, having distinct claws, and the inner branch twice as 
löne vas the outer; Second pair of feet (PI. IV: Eigi 7.) has 
changed so that the outer branch is two-jointed and has received 
one seta more in the upper part of the inner margin; the 
proximal of the three spines on the outer margin is now situated 
on the first joint. The appearance ofthe inner branch is unchang- 
ed: The! new-formed third pair: of feet (Pl: IV. Fig. 8.) is al: 
most entirely similar to the second pair of feet of the young 
in the preceding stage, the only difference being that the outer 
branch has two spines instead of three on its external mar- 
gin. Fourth and fifth pairs of feet wanting. 
In the third cyclops-stage, the body of the young has seven 
free seoments. Anterior antenne (Pl. IV. Fig. 9.) now have three- 
jointed basal pieces, although the second joint is very indistinct- 
ly separated from the third, and thus seven joints in all. Poste- 
rior antenne and first pair of feet having the same shape as be- 
fore. The inner branch of the second pair of feet (P1. IV. 
Fig. 10.) one-jointed and having one seta at the apex as in the 
preceding stages; outer branch having received one spine 
more at the outer margin and one seta more in the inner 
margin of the terminal joint. The inner branch of the third 
pair of feet (Pl. IV. Fig. 11.) now having two sete at the 
apex, the outer branch two-jointed and completely resembling 
