v CRUSTACEA OUTER ORGANISATION 309 



shortened. The anterior antennae of the Cirripcdia (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 Rhizoccphala. In all Cirripedcs, however, 

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

 forms (the Nauplius and the so-called C'ypris-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 protopoclite. The shaft, with its many -jointed flagellum, corresponds 

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



Malacostraca. Here also the anterior antennae 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 Malucostmcan 

 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 Nauplhis larva which 

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

 being always uniramose. 



b. The Posterior Antennae (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 protopoclite, an outer branch 

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

 form in many Entornostraca, 



Entomostraca. Among the Phyllopoda the posterior antennae appear in the 

 Cladoccra as strong biramose rowing antennre (Fig. 192). In Apus they are reduced, 

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

 [iri/lcc and Cyprinidcc they are biramose swimming feet. The exopodite is, however, 

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

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

 posterior antennae of most Copcpoda 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 Copcpoda, however, they appear degenerated 

 into short simple clinging hooks (Fig. 210, E], The posterior antennae are always 

 wanting in adult Cirripedcs, 



Leptostraca (Nebalia) (Fig. 196). The posterior antennae 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 antennae is to be 

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



