APPENDAGES AND NERVOUS SYSTEM OF APUS CANCRIFORMIS, 545 
Two pairs in front of the mouth—* przoral appendages.” 2. 
Three pairs of jaw-legs, more especially related to the pur- 
poses of the mouth as jaws, and immediately following it— 
“oral appendages.” 38. Eleven pairs of variously modified 
but essentially locomotor legs, placed one on each of the eleven 
body segments, in front of and inclusive of the segment car- 
rying the genital apertures—“‘ thoracic appendages.” 4. 
Kifty-two pairs of locomotor legs, gradually diminishing in 
size, and posterior to the genital apertures (less numerous in 
incompletely-grown specimens)—‘“‘ abdominal appendages.” 
They are more numerous than the annulations of the integu- 
ment of this region of the body, which are only seventeen in 
number, but they correspond in number with the ganglionic 
enlargements of the nerve cord.! There are four annulations 
of the body posterior to these appendages, and devoid of a 
continuation of the nervous axis, as well as of appendages. 
A fifth post-pedal segment is perforated by the anus, and 
carries a pair of jointed setose appendages, which may or 
may not be equivalents of the legs of the anterior region. 
The two pairs of appendages in front of the mouth—Both 
these pairs of appendages are of small size—relatively very 
much. smaller than they are in the newly-hatched larva. 
The second pair is much smaller than the first, although 
in the larva the reverse relation obtains. Moreover, the 
second pair, like the first, are simple filamentous tactile 
organs; although in the larva they are powerful biramose 
swimming legs. In the adult Apus, therefore, not only with 
reference to their homology with the corresponding appen- 
dages of the lobster, but alsoin view of their function, these 
two pairs of appendages are entitled to the names anten- 
nules (1st) and antennz (2nd) respectively. 
It appears to be desirable, in order to arrive at true con- 
clusions with regard to the homologies of the limbs of the 
Arthropoda, to abandon altogether the use of such terms as 
“antenna,” “ mandible,” and “‘ maxillipede,”’ as homological 
categories, and to apply them merely as descriptive terms 
proper to the particular case under examination. In the 
consideration of homologies the appendages should be re- 
garded simply as first, second, third, and so forth, without 
the introduction of terms calculated by their reference to 
function to prejudice the argument as to homology. The 
first appendage of an Arthropod A. may be homologous 
with (or homogenous with) the first appendage or with the 
’ The first four post-genital body-rings carry five pairs of legs, the next 
four carry ten pairs of legs, the next four thirteen, the last five leg-bearing 
hody-rings carry twenty four, as nearly as can be estimated. 
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