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specimens of the same species, and it is proportionately somewhat 
shorter and broader in immature specimens than in adult ones; if 
this branch is very long, its flagellum is proportionately short, and 
vice-versa. The lower branch has two flagella which never are 
absolutely equal in length, and often the one of them is more 
than twice as long as the other; the proportion between their 
length seems to be very constant in each species and presents an 
exceedingly practical character. In all species of Pauropus the 
posterior branch is at least slightly, generally somewhat longer than 
the anterior, while the anterior is the longest in the other genera 
hitherto known. The branch itself presents a corresponding cha- 
racter; in Pauropus its anterior margin is at least a little and 
often rather considerably shorter than the posterior, the anterior 
distal angle of the branch bring obliquely and less or more broadly 
cut off; in Stylopauropus, Brachypauropus and Eurypauropus (sens. 
lat.) the anterior margin of the branch is longer than the posterior, 
its posterior distal angle being more obliquely cut off than the an- 
terior one, and in Stylopauropus the branch is distally produced 
into an oblique elongation bearing the anterior flagellum on its 
end, while the posterior flagellum is attached a good deal nearer 
to the base. On the lower surface of the branch is always inserted 
a single hair, the structure of which sometimes presents a specific 
Character. The basal part of the flagella is never ringed, but 
the length of this part is scarcely as valuable as hitherto believed, 
it being somewhat longer in Pauropus siamensis than in the other 
species of this genus. — The globulus is generally described as 
either stalked or sessile, in reality it always has a stalk, which 
often is short or very short; in Pauropus Huxleyi I have found 
its length varying considerably, but nevertheless the length is of 
generic value, as in Pauropus it is never longer than the transverse 
diameter of the globulus, while it is somewhat to several times 
longer than this diameter in the other genera. 
Body. Its general morphology is well known. 
(the head excepted) of twelve segments; the first of these has ve- 
It consists 
