PACKARD.] MORPHOLOGY OF PHYLLOPODA. 387 
In the Apodide no traces have yet, been discovered of the second max- 
ille. 
In the Branchipodide they are present. Spangenberg figures them in 
Branchipus stagnalis as a pair of single elongated oval appendages, very 
minute, and ending in a long setose bristle, with a group of smaller 
sete on the inside near the middle, next to the first maxille. 
Gissler has figured them in Streptocephalus texanus (Plate XXXIV, 
fig. 6m”), where they are represented as oval bodies, with two set, hay- 
ing nearly the same form as in the adult Branchipus stagnalis, but less 
setose. 
The maxillipedes.—These organs, which are here called maxillipedes 
because they bear a gill, arecharacteristic of the Apodidew alone. Nosuch 
appendages have been found in the Limnadiade or Branchipodide, and 
thus those of the Apodide may yet be proved to be homologues of the 
second maxillz of those two families, true second maxill# not existing 
inthe Apodide, though it should be borne in mind that they constitute 
in the Apodide the second pair of appendages behind the mandibles, 
and thus occupy the place of the second maxillz 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 himalayanus. 
We have also found them in Lepidurus couesii and L. bilobatus, 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 other process is an 
oval chitinous plate, with long marginal setze (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 
Claus gives but a very slight allusion to the early condition of this ap- 
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 absence of the 
endite of the maxillipedes, and in the nearly obsolete second antenna, 
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 Lep- 
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 thoracic feet or benopods.—Although the differences between the 
first eleven pairs of feet and those succeeding in the Apodide, or the 
thoracic feet and so-called abdominal feet in the Limnadiada, 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- 
podide, 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 (bwnosomal). We will, then, in this 
paper consider the external opening of the oviduct in the female, and 
