208 THE ANATOMY OF INVERTEBRATED AKIMALS. 



Fig. bi—Protida Thjsteri. A, the Bexual. mature animal, extracted from its calca- 

 reous tube : a, branchial plumes ; b, hood-like expansion of the anterior end of the 

 bofly : c, the mouth ; c?, the stomach ; e, the anu^ ;/, the testos ; g^ the ova. B^ 

 a Protula in course of proliferation ; &, the branchiae of the zo5id, 



bod}', and its walls are very thick and muscular. At its an- 

 terior extremity it is surrounded with a circle of small papil- 

 lae, immediately behind which are four strong, pointed and 

 curved horny teeth, implanted in the muscular wall (Fig. 52, 



