504 PYCNOGONIDA _ CHAP. 
limbs of five joints; and lastly, on the ventral side, some 
little way behind these, we find the ovigerous legs that we have 
already seen in the male Pycnogonwm, but which are present in 
both sexes in the case of Nymphon. At the base of the claw 
which terminates each of the eight long ambulatory legs stands 
a pair of smaller accessory or “auxiliary” claws. The genera- 
tive orifices are on the second joint of the legs as in Pycnogonum, 
but as a rule they are present on all the eight legs in the female 
sex, and on the two hindmost pairs in the male. One of the 
Antarctic Nymphonidae (Pentanymphon) and one other Antarctic 
genus less closely related (Decolopoda) have an extra pair of legs. 
No other Pycnogon, save these, exhibits a greater number of 
appendages than Mymphon nor a less number than Pycnogonum, 
nor are any other conspicuous organs to be discovered in other 
genera that are not represented in these two: within so narrow 
limits le the varying characters of the group. 
In framing a terminology for the parts and members of the 
body, we encounter an initial difficulty due to the ease with 
which terms seem applicable, that are used of more or less 
analogous parts in the Insect or the Crustacean, without warrant 
of homology. Thus the first two pairs 
of appendages in Wymphon have been 
commonly called, since Latreille’s time, 
the mandibles and the palps (Linnaeus 
had called them the palps and _ the 
antennae), though the comparison that 
Latreille intended to denote is long 
abandoned; or, by those who leaned, 
with Kroyer and Milne - Edwards, to 
the Crustacean analogy, mandibles and 
maxillae. Dohrn eludes the difficulty 
apres eet Sk by denominating the appendages by 
below, showing  chelo- simple numbers, 1 ie EE Vier AAU KS 
ee palps, and oviger- ond this method has its own advantages ; 
but it is better to frame, as Sars has 
done, a new nomenclature. With him we shall speak of the 
Pycnogon’s body as constituted of a trunk, whose first (composite) 
segment is the cephalic segment or head, better perhaps the 
cephalothorax, and which terminates in a caudal segment or 
abdomen; the “head” bears the proboscis, the first appendages 
