330 



INVERTEBRATE MORPHOLOQT. 



be obtained. In the majority of forms, however, the arrange- 

 ment is much more complicated than this. Thus in Mytilus 

 it will be found that the various pinnae composing each 

 plate are held together by a series of patches of strong cilia 



au pc 



., ^^^0 

 ^ 



F/Q. 148. — A, diagrammatic section through Pecten, and B, through Anodon,- 



G, section through gill-lamella of Pecten, and D, of Anodon. 

 au = auricle. ol = outer lamella of outer gill. 



/ = foot. pc = pericardial cavity. 



gf = gill-filament. p = pore. 



ill = inner lamella of inner gill. s = blood-siuus. 



il = interlamellar junction. sir = suprabrauchial chamber. 



ne = nephridium. sh = shell. 



which interlock forming the "ciliated junctions," and further- 

 more the pinnsB are at their free ends bent abruptly upon 

 themselves, those of the outer row outwards and those of the 

 inner row inwards, so that each gill-plate is composed of two 

 lamellae (Fig. 148, A). This condition may be regarded as the 

 next step in the modification, which is continued even 

 further by the permanent union of the outer and inner limbs 



