PACKARD.] MORPHOLOGY OF PHYLLOPODA. 387 



In the Apodidce no traces have yet been discovered of the second max- 

 illae. 



In the Branchipodid(B they are present. Spanj^enberg figures them in 

 Brancliipus stagnalis as a pair of single elongated oval appendages, very 

 minute, and ending in a long setose bristle, with a group of smaller 

 setse on the inside near the middle, next to the first maxillae. 



Gissler has figured them in Streptocephalus tcxamis (Plate XXXIV, 

 fig. Gni^), where they are represented as oval bodies, with two setae, hav- 

 ing nearly the same form as in the adult Branchiims stagnalis, but less 

 setose. 



The maxilUpedes. — These organs, which are here called raaxillipedes 

 because they bear a gill, are characteristic of the Apodidw alone. No such 

 appendages have been found in the Limnadiadce or Brancliipodidw, and 

 thus those of the Apodidce may yet be proved to be homologues of the 

 second maxillae of those two families, true second maxillae not existing 

 in the Apodidw, though it should be borne in mind that they constitute 

 in the Apodidce the second pair of appendages behind the mandibles, 

 and thus occupy the place of the second maxillae of the two other Phyl- 

 lopodous families. 



The maxillipedes of Apus cancriformis have been described and well 

 figured by Lankester ; we have found them as he describes in our speci- 

 mens of this species, and also in Apus Mmalayanus. 



We have also found them in Lepidurus couesii and L. hilohatus, the 

 spiny inner appendage or first endite corresponding to the maxilliform 

 coxal lobe (gnathobase of Lankester) of the succeeding feet. 



Lankester says of this endital portion of the appendage, after speak- 

 ing of the gill, or what he calls the " bract," " The ot.her process is an 

 oval chitinous plate, with long marginal setae {en') ; it may possibly 

 represent the flabellum, but more probably one of the endites, perhaps 

 endite 1 (the gnathobase). There is no means of deciding this point, for 

 Glaus gives but a very slight allusion to the early condition of this aj)- 

 pendage in his account of the development of Apus." 



On carefully examining our four American species of Apus, none 

 were found to have the endite of the maxillipedes present, only the gill 

 or exite being developed. It thus appears that in the aljsence of the 

 endite of the maxillipedes, and in the nearly obsolete second antennae, 

 the American species of Apus have advanced, so to speak, a step farther 

 than the Old World species of the genus, which have retained the Lepi- 

 durus condition; and in this respect as well as in the smaller carapace 

 and the longer abdomen, the genus Apus stands above Lepidurus. The 

 history of the maxillipede in the development of the early stages needs 

 special research, as it will be most interesting to learn the date of its 

 appearance, its structural changes during the metamorphosis of the 

 individual, and the final disappearance of the endite in the American 

 species. 



The tlioracie feet or hcenopods. — Although the differences between the 

 first eleven pairs of feet and those succeeding in the Apodidce, or the 

 thoracic feet and so-called abdominal feet in the Limnadiadw, are but very 

 slight, and they mainly differ as regards the abdominal members, in hav- 

 ing genital openings situated upon one (the anterior) pair, so that on the 

 whole the distinction seems artificial, yet when we ascend to the Branchi- 

 podidce, where the abdomen is differentiated from the thorax, and has 

 but a single pair of appendages (the gonopoda), it is easy to see that all 

 the members in front of the external reproductive appendages may be 

 properly designated as thoracic (baenosomal). We will, then, in this 

 jjaper consider the external opening of the oviduct in the female, and 



