PACKAED.] MOEPHOLOGY OF PHYLLOPODA. 385 



SO far as my observations go. I have found them always present 

 in full-grown specimens of Apus cancriformis from Munich, from Prag, 

 and from Padua." 



In specimens of Apus cancriformis kindly sent us by Professor Sie- 

 bold, of Munich, we have found the second antennae to be inserted on the 

 inner declivity of the frontal doublure forming the front of the head, 

 and inserted iDehind the first antennae, and farther out from the labram 

 than the first antennae. They are in form as described and figured by 

 Lankester. I also found them in my examples of Apus Mmalayamis, and, 

 as in A. cancriformis, they are larger and more easily found than in the 

 American species. 



On looking for the second antennae in our American species I was at 

 first unable to find them, they were so minute and so closely appressed to 

 the body. In specimens of Lepidurus couesii which were well preserved 

 the antennas were found, but none in L. bilohatus, of which I had but two 

 indifferently preserved specimens. Figs. 2&, 2c, of Plate XXXII, show 

 their relative size in Apus lucasanus, both being drawn to the same 

 scale. In order to find them the mandibles have to be forcibly moved 

 backward. They were also found in Ajnis newberryi, A. wqualis, and in 

 A. longicaudatuSj but in all these American species they are mnch smaller 

 and more difi&cult to find than in the European and Asiatic species ; a 

 point of some interest, which coupled with the greater obsolescence o^ 

 the maxillipedes and the smaller carapace shows that the American 

 species have reached a stage farther removed from the larval condition 

 than the Old World forms. 



Histology. — The histological structure of the 2d antennae of the Limna- 

 diadw is shown at fig. 2, Plate XXIX, which represents the three terminal 

 joints of one of the llagella of the second antennae of JEstheria. The joints 

 are seen to be crowded with nerves of specialsense, and the antennal nerve 

 is seen to terminate in fibers, one of which passes into each seta ; so that 

 these organs must be highly sensitive, perhaps only tactile, however, 

 while they are also rowing or swimming organs. 



TJie mandibles. — All Phyllopoda have well-developed mandibles, ex- 

 cept in the highest or most specialized family, the Brancliipodidoi, in 

 which they are weak and feeble in function, though with primarily the 

 form common to the group. 



In the Limnadiadw (according to Lilljeborg), in Limnadia gigas, and as 

 we have observed in the Apodidw, the mandibles are without a palpus in 

 the adult, and are solid chitinous appendages with the biting edge either 

 snaooth, as in Limnadiadw, or provided with strong smnte, teeth as m 

 Lepidurus and Apus. (Plate XXI, figs. 11, 12.) 



When we look at the larval mandibles of Ap^is, which are represented 

 by Dr. Gissler (Plate XXXY, fig. 1, md), it is not only plain that 

 they are the third and last pair of the limbs of the Xauplius, but it is 

 also plain that the mandible originally consists of two portions, the 

 basal joint with its masticating edge and the two-jointed palpus; this 

 palpiform appendage becomes absorbed or at any rate disappears in the 

 two families under consideration, and it is easy to see that the mandible 

 proper represents or is the homologue of the basal joint of the axis of 

 the limb, together with the first endite, coxal lobe, or gnathobase of the 

 adult Limnadiad or Apodid leg (e. g., Plate V, figs. 5 1\ la ; Plate XXI, 

 fig. Acl). 



In the Apodidae the cutting edge of the mandible is provided with 

 eight or nine teeth, which are naturally less blunt in the adult than in 

 the larva (see Plate XXXV, fig. 4, 4a palpus). 



In the Branchipodidw the mandibles, as shown by Spangenberg (suppl. 

 25 H 



