244 MANUAL OF ZOOLOGY. 



Order II. Ascidia abdominalia. 



Alimentary canal completely behind the branchial sac, which is com- 

 paratively small. (Salpa, Doliolum, $c.) 

 Order III. Ascidia larvalia. 



Permanent larval form. (Appendicularia.) 



The following subdivisions are those adopted by Mr. Wood- 

 ward. 



CLASS TITNICATA. 



Fam. I. Ascidiada (Simple Ascidians). 



Animal simple, fixed, solitary or gregarious ; oviparous ; sexes 

 united; branchial sac simple, or disposed in (8 18) deep and regular 

 folds. 

 Fam. II. CUwettinida (Social Ascidians). 



Animal compound, fixed; individuals connected by creeping tubular 

 prolongations of the common tunic through which the blood circulates, 

 (or by a common gelatinous base). Keproduction effected by ova, or 

 by gemmation from the common tube ; the new individuals remaining 

 attached to the parent, or becoming completely free. 

 Fam. III. Botryllida (Compound Ascidians). 



Animals compound, fixed, their tests fused, forming a common mass 

 in which they are imbedded in one or more groups. Individuals not 

 connected by any internal union ; oviparous and gemmiparous. 

 Fam. IV. Pyrosomid(B. 



Animal compound, free and oceanic. 

 Fam. V. Salpida. 



Animals free and oceanic ; alternately solitary and aggregated. 



CHAPTER XLIV. 



BKACHIOPODA. 



CLASS III. BRACHIOPODA (PaUiobranchiata'). The members of 

 this class are denned by the possession of a body protected by 

 a bivalve shell, which is lined by an expansion of the integu- 

 ment, or ' mantle,' The mouth is furnished with two long 

 cirri ferous arms. The nervous system consists of a single 

 ganglion, placed in the re-entering angle between the gullet 

 and the recfcum, so that the intestine has a ' neural flexure.' 



The Brachiopoda are essentially very similar in structure to 

 the Polijzoa, from which they are distinguished by the fact 

 that they are never composite, and by the possession of a 

 bivalve, calcareous, or sub- calcareous shell. They are com- 

 monly known as 'Lamp-shells,' and are all inhabitants of the 

 sea, being sometimes free, but being more commonly attached 

 to some solid object. From the presence of a bivalve shell, 

 the Brachiopods have often been placed near the true bivalve 



