54 ZOOLOGY. 



Excellent figures of this group are given bj Milne Edwards, in the 

 illustrated edition of the Eegne Animal, and by Johnston. The following 

 genera of Escharidss are figured on X->^. 75 : Fhistra {fig. 54), Reiepora 

 {fig. 5G), and Eschara {fig. 5"). The following classification is that of 

 Johnston : 



^Natives of the Sea, Tentacula forming a perfect circle. Polypiaria 

 infuiidihulati., P. Gervais. Fams. 1 to 0, 



**Lacijsteine. Tentacula in the form of a horse-shoe. Polypiaria 

 hippocrepia., P. Gervais. Fam. 7. 



Fain. 1. Yesicularidcc. Corneous, fistular, confervoid ; cells vesicular, 

 deciduous, not operculote. Yesicularia, Scrialaria, Yalkeria, Baverbancia. 



Fam. 2. Crisiada. Calcareous, branched, confervoid, jointed; cells 

 linked together in series, distinct, tubular, or elliptical, with a terminal or 

 subterminal aperturS ; no operculum. Crisia, ISTotamia, Hippothoa, 

 Anguinaria. 



Fam. 3. Tuhdip>oridce. . Calcareous, variable in shape, never confervoid ; 

 cells tubular, round, rising from a base and projecting, aperture terminal 

 and non-operculate. Tubulipora, Discopora. 



Fam,. 4. Celleporidce. Calcareous, lobed, ramous, or crustaceous ; cells 

 in quincunx, utricular, in juxta-position, with a contracted terminal aperture. 

 Cellepora, Lepralia, Membranipora. 



Fam.. 5. Fscharida'. 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, Eetepora, 

 Eschara. 



Fam. 6. Alcyonidnke. Polypidoms sponge-like, polymorphous ; cells 

 irregular in disposition, immersed and concealed, with a contractile non- 

 operculate aperture. Alcyonidium, Cliona. 



Fa7n. 7. Zimniades. Polypidoms fleshy, spongy or corneous, polymor- 

 phous ; animals in tubes with angular or round orifices, closed when they 

 recede. Cristatella, Plumatella. 



Oedee 2. TuNicATA. Thesc animals, especially Aseidia {pi. 77 ., 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 tough 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 branchiae 

 by the action of the vibrillie, 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 



