v CRUSTACEA OUTER ORGANISATION 309 



shortened. The anterior antennae of the Cirripedia (Figs. 205 and 207) are very 

 small, and can no longer be called limbs. The cement glands, whose secretion serves 

 for fastening the body to the surface it rests on, open on them. These antennae, as 

 well as all other limbs, are wanting in the Rhizocephala. In all Cirripedes, however, 

 even in the Rhizocephala, they are well developed in the free-swimming young 

 forms (the Nauplius and the so-called Cypris-like larva). 



Leptostraca. In Nebalia (Fig. 209, C) the antennules are well developed. They 

 consist of a 4 -jointed shaft which carries two appendages, one in the form of a plate ; 

 the other, which is slender and flagellate, has many joints and carries olfactory 

 filaments. These two appendages can in no wise be considered as the exopodite and 

 endopodite of a biramose limb, as these latter always arise from the 2d (distal) joint 

 of the shaft or protopodite. The shaft, with its many-jointed flagellum, corresponds 

 with the undivided uniramose antenna. The plate is a new formation. 



Malacostraca. Here also the anterior antennas are well developed and provided 

 with olfactory filaments. They usually consist of a 3- or 4-jointed shaft and 2 

 flagella, one of which (accessory flagellum) is a secondary production of the 

 antennule (Fig. 209, A}. There are sometimes 2 accessory flagella, and some- 

 times they are altogether wanting (Isopoda), and in this latter case the antennule 

 shows its typical uniramose form (Fig. 209, B}. The form of the Malacostracan 

 antennules varies very much in details ; it shows more or less considerable variations 

 in the two sexes. That the antennules of the Malacostraca also were originally 

 uniramose as opposed to all the other biramose appendages, and that the accessory 

 flagella are new formations, is principally proved by the Nauplius larva which 

 occurs in some of the Malacostraca ; its first pair of limbs (the later antennules) 

 being always uniramose. 



b. The Posterior Antennse (Fig. 210). 



These correspond with the 2d pair of limbs of the Nauplius, being 

 its first pair of biramose limbs, and often serve as feelers. They' con- 

 sist typically of the 2- jointed shaft or protopodite, an outer branch 

 (exopodite) and an inner branch (endopodite). They appear in this 

 form in many Entomostraca. 



Entomostraca. Among the Phyllopoda the posterior antennae appear in the 

 Cladocera as strong biramose rowing antennae (Fig. 192). In Apus they are reduced, 

 and in Branchipus transformed into pincers. Among the Ostracoda in the Halocy- 

 pridve, and Cyprinidce they are biramose swimming feet. The exopodite is, however, 

 considerably reduced, and in the male supplied with seizing hooks. In the Cypri- 

 didce and Cytheridce, however, they are uniramose, i.e. without exopodite. The 

 posterior antennae of most Copepoda are clinging organs. In a few free-living forms 

 they are typically biramose (Fig. 210, D\ in others uniramose, consisting of several 

 joints (Fig. 210, C}. In the parasitic Copepoda, however, they appear degenerated 

 into short simple clinging hooks (Fig. 210, JE). The posterior antennae are always 

 wanting in adult Cirripedes. 



Leptostraca (Nebalia) (Fig. 196). The posterior antennas consist of a 3-jointed 

 shaft and a many-jointed flagellum, which is unusually long in the male. The exo- 

 podite is wanting. 



Malacostraca. In this division the posterior antennae is very commonly a 

 5-jointed shaft and a thin (ringed) many-jointed flagellum, the 2d joint of the 

 shaft carrying a scale (squame). This structure of the posterior antennas is to be 

 explained as follows. The first 2 joints of the shaft answer to the protopodite, 



