Ldrrnl Sfdijes nf Triloltifcs. — Beerlicr. 189 
is passed within the egg. Even a more marked reduction is ex- 
liibited in the embryos of Pala'mon and u4.v^/l:■/^s• (figures 25 and 
26). ( 'n clops is a very normal form, 'though even here in a sec- 
ond naiiplius stage (figure 12), a fourth pair of limbs is devel- 
oped. 
Exam])les have been cited showing the reduction and obso- 
lescence of the anterior antenna', or first pair of naiiplius limbs, 
and some cases will now be cited in which the third pair also 
becomes reduced and rudimentary. Arhf /teres (figure 14) and 
J///.S/.S- (figure 22) afford instances of this variation. The for- 
mer is of additional interest, as showing that the appendages 
from the fourth to the eighth, may be developed, while the third 
remains quiescent, and that the second pair, tjqjicall^'^ biramous, 
is here unbranched. Similarl}", in JIi/sis\ Xehah'd (figure 19), 
and especially in Ci/jiris (figure 18), the nauplius limbs are 
simple. The embryo of Lucifer (figure 24) and a late nauplius 
stage of EnplKtiisId (figure 21) are also of moment, in showing 
the beginnings of the metastoma (//'/) with the two maxillaj 
and first maxilli])edes. 
It appears fron) the foregoing facts, tiiat euougli has been 
shown to prove th« marked variations in the number and state 
of development of the nauplius appendages, and to reach the 
conclusion, that potentially five i)airs of cephalic appendages 
are present. The two posterior ])airs are the ones usiuilly not 
developed until after some of the trunk limbs appear. Very 
satisfactory explanations have been offered as to why the first 
three pair*< have been selected by the larva, although it does not 
seem to have been recognized that the fourth and fifth iiave 
been more or less suppressed during the evolution of the class. 
Lang'--5 accounts for the three pairs of iiaupliaii limbs by say- 
ing that: "In a young larva whicli, like the Xfiirpliiis, is 
hatched early from the egg, only a few of the organs most nec- 
essary for independent life and independent ac(|iiisition of food 
can be developed. The 3 most anterior pairs of limbs which 
serve for swimming may Ije described as such most necessary 
organs. The third pair perhaps belongs to tiiis category, be- 
cause as mouth parts, generally i)rovided with masticatory pro- 
cesses, they serv<' not only witn the others for locomotion, hut 
also for conducting footi to the oral aperture."' 
Allot her point in favor of the original pentamerons eoniposi- 
