54 ZOOLOGY. 
Excellent figures of this group are given by Milne Edwards, in the 
illustrated edition of the Régne Animal, and by Johnston. The following 
genera of Escharide are figured on pl. 75: lustra (fig. 54), Retepora 
(fig. 56), and Lschara (fig. 57). The following classification is that of 
Johnston : 
*Natives or THE Sea. Tentacula forming a perfect circle. Polypiaria 
infundibulati, P. Gervais. Hams. 1 to 6. 
**TacustRInE. Tentacula in the form of a horseshoe. Polypiaria 
hippocrepia, P. Gervais. Lam. 7. 
Fam. 1. Vesicularide. Corneous, fistular, confervoid; cells vonage! 
deciduous, not operculate. Vesicularia, eS seillcerias Baveeiaue es 
Fam. 2. Crisiade: Calcareons, biwaeen confervoid, jcmee cells. 
linked together in series, distinct, tubular, or elliptical, with a terminal or 
subterminal aperture; no operculum. Crisia, Notamia, Hippothoa, 
Anguinaria. 
Ham. 3. Tubuliporide. _Calcareous, variable in shape, never confervoid : 
cells tubular, round, rising from a base and projecting, aperture terminal 
and non-operculate. Tubulipora, Discopora. 
Fam. 4. Celleporide. Caleareous, lobed, ramous, or crustaceous; cells 
in quincunx, utricular, in juxta-position, with a contracted terminal aperture. 
Cellepora, Lepralia, Membranipora. 
Fam. 5. Escharide. Calcareous or membranous, variable ; cells usually 
in quincunx, oblong, pentagonal, or hexagonal, conjunct, immersed, or 
horizontal to the plane of axis, with a subterminal or lateral, and commonly 
operculate aperture. Flustra, Cellularia, Acamarchis, Farcimia, Retepora, 
Eschara. 
Fam. 6. Alcyonidulew. Polypidoms sponge-like, polymorphous; cells 
irregular in disposition, immersed and concealed, with a contractile non- 
operculate aperture. Alcyonidium, Cliona. 
Fam. 7. Limniades. Polypidoms fleshy, spongy or corneous, polymor- 
phous ; animals in tubes with angular or round orifices, closed when they 
recede. Cristatella, Plumatella. 
Orver 2. Tuntcata. These animals, especially Asczdia (pl. TT, figs. 7, 8) 
and its allied forms, may be compared to bivalve mollusca or conchifera, 
in which the margins of the mantle are united so as to form a sac, in 
which two openings are left, one for alimentation and respiration, and the 
other for excretion. The mantle is of a tongh coriaceous or cartilaginous 
texture, and is endowed with contractility. Cellulose, which is almost 
exclusively found in plants, has been ascertained to enter into the 
composition of the Tunicata. A current is made to flow over the branchize 
by the action of the vibrilla, and the contractions and expansions of the 
body remove the water. 
The Tunicata have no external organs of locomotion, so that they float 
about at random, or are fixed to rocks, sea-weed, or other extraneous 
bodies. Some species are agglutinated together in masses, or in long 
chains, but there is no organic connexion between them. 
This order includes three families represented by the genera Salpa, 
258 
