HOMOLOGIES OF THE CRUSTACEAN LIMB. All 
-as is so well marked in the maxillipedes, and the thoracic lees possess 
not even the rudiments. Change of function and radical changes of 
structure are most extreme in the 
Malacostracous Crustacea, from the 
Brachyura tothe Isopoda and Am- 
phipoda. If sostartling in these com- 
_paratively recent forms, it is not to 
be wondered at that still greater and 
-more fundamental modifications of 
.the Crustacean type obtain in the 
archaic forms, the Paleocarides, of 
‘which Limulus is the sole survivor. 
-To those who insist on the Arachni- 
dan affinities of the Merostomata, we 
_would suggest that the same shifting 
_and change of function and structure 
is to be observed among the Trache- 
ate Arthropoda, and that Limulus is 
not less a genuine Branchiate Ar- 
thropod for presenting some features 
analogous to the Arachnida. 
A study of the Phyllopoda and 
Phyllocarida must tend to confirm 
the view we have expressed as to the 
synthetic, or generalized nature of 
Limulus, while we have in another 
‘place endeavored to show in the 
light of A. Milne—Edwards’ anatom- 
ical studies on Limulus, that it is 
an abnormal Crustacean and far re- 
moved from the Branchiopoda; there 
are nevertheless some points in which 
it comes in contact with the Phyllo- 
poda, and which have been noticed 
ever since the time when O. I*. Muller 
comprised Apus in his genus “ Limu- 
lus.” If the reader will compare the 
accompanying longitudinal section of 
Limulus with our section of Apus 
in Pl. XX XVII, some striking resem- 
blances will be seen; externally the \ 
front edge of the carapace, 2. e., the \ 
frontal doublure, so well adapted for 
burrowing in the mud; the relations 
of the hypostoma or labrum, and the 
retention of the ocelli, as well as the 
mode of moulting the shell, are ex- 
ternal points of resemblance, while , Fc. 41 Sestion thronalia small Limutuspoly. 
internally the front part of the head caridous Crustacean suchas Apus: liv, liver; pr, 
filled with the lobules of the: liver, [i?nous plate over ihe nerrous eyetem, ine, 
the oblique, long, narrow, cesopha- intestine; 4, ANUS 5 br, brain; m, mouth; or, 
: 4s > : @sophageal ring; ng, abdominal ganglia. 
gus, the position of the stomach under 
the eyes so far in front in the head, the simple archi-cerebrum, the gen- 
eral form of the heart, and the gnathobases near the mouth are addi- 
tional points of resemblance. 
