PACKARD.] MOKPHOLOGY OF PHYLLOPODA. 373 



abdomen, and it is not uutil we ascend to the Brancliipodidcs that we 

 meet with a well-marked abdomen. sei)arated 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 antennce, which are in the adult preoral ; 

 second, the organs of prehension of food and of masticatibn, *. e.,the man- 

 dibles and accessory jaws, or maxilli© and maxillipeds, which are post- 

 oral ; third, organs of locomotion, whether natatorial or ambulatory, 

 Avhich 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 Branehipics 

 stagnaUs^ 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 ap])endages 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 Apodid£e, 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 BrancMpodidm 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 Clans. 



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 applj^ them merely as descriptive terms proper to the 

 particular case under examination. In the consideration of homologies, 

 the appendages should be regarded simply as first, second, third, and 

 so forth, without the introduction of terras 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 in<licate 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." 



* I have (American Naturalist, xv, p. 831, 1881) applied the term rjonopoda (Gr. yovi), 

 geiieratiou ; Ttov?, TtoSoi, foot) to the first aud secoud 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 nse in descriptive carcinology when 

 speaki*ng of either or both pairs of the basal abdominal limbs of the male Decapod. 

 In the female they are not modified. 



