Introduction to A nimal Morphology. 2 4 1 



the common cloaca, the abdomen not sharply marked off; 

 they may be regularly arranged (Botryllus) in stars or discs, 

 or irregularly (Botrylloides). (B.) Didemninse having the 

 body divided into thorax and abdomen, and each embryo 

 producing two individuals. In Leptoclinum there are few 



is pud a ?ix-lobed mouth. Encoelium has many systems 

 and an obsolete!}* rayed mouth. Didemnium has many 



is and a pedunculate abdomen. Distomus has one or 

 more circles of personoe, and each has a six-rayed mouth and 

 anus. Diazona has regular concentric circles of persona? 

 forming a rosette-like disc. (C.) Polyclininaa body with 

 not only a thorax and abdomen, but a post-abdomen, con- 

 taining the heart. Polyclinum has apedunculated post-abdo- 

 men ; the mouth is six-rayed ; the anal opening prolonged 

 horizontally and irregularly cut. Aplidium has the anal 

 opening indistinct, and no central cavity. Sidnyum has an 

 eight- toothed branchial opening, and a simple, tubular, folded, 

 anal opening. Synoicuin has a six-rayed mouth, an irregu- 

 larly six-rayi-d anus, and a sessile post-abdomen. Amouro- 

 cium has indistinct abdominal divisions; mouth six-rayed. 

 In Farascidium the mouth is eight-rayed, with two eye-specks. 

 Sigillina is seal-like, the narrowing circlets rising one over 

 ano: 



CHAPTER XXXIV. 



SUB-KINGDOM 6. MOLLUSCA (Cuw'cr}. 



MOSTLY aquatic, soft-bodied persoiur, compos- 

 on'-, two, or three obscurely marked metanirres, with 

 aeon- ibt'Tal svmmetry. Their structure can 



ily understood by regarding- them as Venues* 



\Vck iow as yrt of no alolutc passage forms or direct synthetic 



R 



