136 

 Plate IX. 



Figf. 4G. Dorso-ventral sectioii of small P. operculans, 

 through, centre of adductor. x 5. 



Fig. 47. Section of small P. opercularis (same plane as 

 fig. 46), through digestive gland and anterior 

 end of adductor. x 5. 



Fig. 48. Section of small P. opci-cuLtris (same plane), 

 anterior to adductoT muscle through visceral 

 mass. X 5. 



Fig. 49. Section of wall of auricle, showing the excre- 

 tory cells of pericardial gland. Zeiss apo. 1*5. 



Fig. 50. Section of digestive gland, showing alveoli with 

 pigment, and digestive ducts. x 170. 



Fig. 51. Trans, section through renal organ. x 50. 



Fig. 52. Part of previous section more highly magnified. 



X 400. 

 Fig. 53. Section through ovigerous and seminal alveoli 

 of gonad (almost ripe). x 200. 



Fig. 54. Striped muscle fibres from adductor, in surface 

 (b) and edge view (c). Zeiss apo. 1*5 mm 



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