CfLETOPODA. 



337 



behind the mouth, in the larva of Terebella conchilega 

 (Claparede). 



Mitraria. A peculiar larval Ch;etopod form known as Mitraria^the 

 metamorphosis of which was first worked out by Metschnikoff, deserves a 

 special notice. 



This form (fig. 155 A) in spite of its remarkable appearance can easily be 

 reduced to the normal type of larva. 



The mouth (m) and anus (an) (fig. 155 A) are closely approximated, and 

 situated within a vestibule the edge of which is lined by a simple or lobed 

 ciliated ring. The shape of the body is somewhat conical. The cavity of 



B 



FlG. 155. TWO STAGES IN THE DEVELOPMENT OF MlTRARIA. 



(After Metschnikoff.) 



m. mouth; an. anus; sg. supra-resophageal ganglion; br. provisional bristles; 

 pr.b. prse-oral ciliated band. 



the vestibule forms the base of the cone, and at the apex is placed a ciliated 

 patch (sg). A pair of lobes (br) bear provisional setae. The alimentary 

 canal is formed of the three normal parts, oesophagus, stomach, and 

 intestine. 



To compare this larva with an ordinary Chastopod larva one must 

 suppose that the alimentary canal is abnormally bent, so that the post-oral 

 ventral surface is reduced to the small space between the mouth and the 

 anus. The ciliated band surrounding the vestibule is merely the usual 

 prae-oral band, borne on the very much extended edge of the prae-oral lobe. 

 The apex of the larva is the front end of the prae-oral lobe with the 

 usual ciliated patch. The two lobes with provisional bristles are really 

 dorsal and not posterior. 



B. II. 



22 



