64 ZOOLOGY. 



Excellent figures of this grouj) are given by Milne Edwards, in the 

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

 genera of Escharid« are figured on jpl. 75 : Flustra {fig. 54), lietepora 

 {fi^. 56), and Eschara {fig. 57). The following classification is that of 

 Johnston : 



*]S[atives of the Sea. Tentacula forming a perfect circle. Polypiarick 

 i nfundihnlati., P. Gervais. Farns. 1 to 6. 



^^Lactstrine. Tentacula in the form of a horse-shoe. Polypiaria 

 h ijypocrejna^ P. Gervais. Fam. 7. 



Fam. 1. Vesicularidce. Corneous, fistular, confervoid; cells vesicular, 

 deciduous, not operculate. Vesicularia, Serialaria, Valkeria, Baverbancia. 



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

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

 subterminal aperture ; no operculum. Crisia, Notamia, Ilippothoa, 

 Anguinaria. 



Fam. 3. Tuhnliporido!. Calcareous, variable in shape, never confervoid ; 

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

 and non-operculate. Tubulipora, Discopora. 



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

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

 Cellepora, Lepralia, Membranipora. 



Fam. 5. Escharida\ 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, Retei)ora. 

 Eschara. 



Fam. 6. Alcyonidnlo?. 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. 



Order 2. Tunicata. These animals, especially Ascidia {2)1- T^.figs. 7, 8) 

 and its allied forms, may be compared to bivalve mollusca or eonchifej-a, 

 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 

 bv 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 



