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, IS, 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. ds. Blood- 

 space, cr. Chitinous rod. llm. Lower longitudinal muscle, su. Sus- 

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

 of a chitinous rod. y. 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 commuuicates with blood-spaces in the 

 mantle. At intervals it commuuicates with similar spaces in 

 the body proper. Unlike the suspensory membrane of Yoldia 

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



