360 



GILMAN A. DREW. 



the sake of completeness^, it would not be necessary to 

 describe it here. Mitsukuri's (11) description of the gill of 

 Nucula proxima holds good in all essentials for the gill of 

 this species^ and since his description was published others 

 have verified and supplemented his results (7^ 13^ and 16) 

 until our knowledge of the structure is comparatively com- 

 plete. 



The adult gill of Nucula delphinodonta is suspended 

 from the body-wall by a fold of tissue, the suspensory mem- 



Text-fig. U.— A pair of plates from a gill of Yoldia limatula. 6s. Blood- 

 space, a: Chitinous rod. Ilni. Lower longitudinal muscle, su. Sus- 

 pensory membrane, ulm. Upper longitudinal muscle, v. Cut surface 

 of a chitinous rod. ^. Cut wall of the gill plate where it bends to join 

 the plate anterior to it. 



brane (fig. 53, gs.), that was originally a fold on the inner 

 surface of the mantle lobe. The suspensory membrane 

 contains between its walls a large blood-space that communi- 

 cates near its anterior end with the auricles of the heart, and 

 throughout its length communicates with blood-spaces in the 

 mantle. At intervals it communicates with similar spaces in 

 the body proper. Unlike the suspensory membrane of Yoldia 

 (Text-fig. U), this membrane is not very muscular, but some 



