PACKARD.] MORPHOLOGY OF PHYLLOPODA. 373 
abdomen, and it is not until we ascend to the Branchipodidz that we 
- meet with a well-marked abdomen separated by tolerably clear indica- 
tions from the thorax. 
THE APPENDAGES IN GENERAL. 
The appendages of Crustacea may be divided into four groups: First, 
the sensory appendages, or antenne, which are in the adult preoral ; 
second, the organs of prehension of food and of mastication, i. é., the man- 
dibles and accessory jaws, or maxille and maxillipeds, which are post- 
oral; third, organs of locomotion, whether natatorial or ambulatory, 
which are appended to the thoracic portion of the body; and, fourth, 
the appendages of the abdomen, which are both natatorial and con- 
cerned in reproduction; of the latter are the two pairs of gonopoda* in 
the Decapoda, while the eleventh pair of appendages in Apus may be 
regarded as gonopods. 
Spangenberg has described the mode of origin of the intromittent 
organs, and has shown that they arise as two independent outgrowths 
from the under side of the twelfth and thirteenth segments in Branchipus 
stagnalis, but from his drawings they appear essentially to arise from the 
twelfth. Each process or finger-shaped lobe contains a cirrus or intro- 
mittent organ. These two appendages appear from Spangenberg’s illus- 
trations to be three-jointed. If so, we do not see why they should not 
be properly regarded as homologous with the eleventh pair of legs of 
male Apodidz, in which, as stated by Gerstaecker, were found the male 
openings for the passage of the semen. We hence regard these organs 
as in general homologous with the gonopods of Decapoda, although the 
latter are solid and do not act as direct intromittent organs. 
It is perhaps as probable, however, that the gonopods or double intro- 
mittent organ of the Branchipodide is homologous with the male organ of 
the Copepoda, which is a double eminence, on each of which is a gen- 
ital pore. The female genital outlet is in the Copepoda also situated on 
the first segment of the abdomen, according to Claus. 
Lankester has suggested, and it seems to us with good reason, that 
in order to arrive at true conclusions with regard to the homologies of 
the limbs of the Arthropoda we should “ 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. Inthe consideration of homologies, 
the appendages should be regarded simply as first, second, third, and 
so forth, without the introduction of terms calculated by their refer- 
ence to function to prejudice the argument as to homology. ‘The first 
appendage of an Arthropod, A, may be homologous with (or homo- 
genous with) the first appendage, or with the second or third of another 
Arthropod, B, and so on; but ambiguity is inevitably introduced if we 
attempt to indicate this homology by the use of such terms as anten- 
nule and antenna, to be applied in both cases alike, for in such cases 
as the parasitic Copepoda, the various Arachnida, and the living and 
fossil branchiate scorpions (Merostomata), these descriptive terms, and 
others like them, are found to be absolutely contrary to fact in their 
implications, and involve also debatable assumptions in reference to 
ancestral primitive forms.” 
*T have (American Naturalist, xv, p. 831, 1881) applied the term gonopoda (Gr. yorvn, 
generation ; zovs, 20605, foot) to the first and second abdominal limbs of the De- 
capoda, which are, as is well known, modified into accessory generative organs., 
The term is suggested as a convenient one to use in descriptive carcinology when 
speaking of either or both pairs of the basal abdominal limbs of the male Decapod. 
In the femule they are not modified. 
