354 G. HAROLD DREW 



tered through it are numerous strands of connective tissue. 

 These contain fibroblasts with very elongated, deep staining nu- 

 clei, and long fibrillar processes. 



The gonad consists of a semicrescentic mass attached at its 

 base to the adductor muscle. When ripe the male proximal por- 

 tion is creamy white in color, and the distal female part is of 

 an orange or vermilion hue; the boundary between the male and 

 female portions is sharply defined. 



In Pecten maximus the loop of the intestine reaches almost to 

 the apex of the ovary, whilst in Pecten opecularis it does not ex- 

 tend much beyond the testis. 



Microscopically the gonad consists of branched tubules, termin- 

 ating in alveoli lined with germinal epithelium : when ripe the 

 alveoli are crowded and distended with ova or sperm, and it is 

 not always easy to trace the connecting tubules. These tu- 

 bules join up to form two main ducts which are lined by columnar 

 ciliated epithelial cells, the height of which is about twice the width 

 while the cilia are about as long as the cells (Dakin). Traced 

 towards the alveoli, the cells lining these ducts become shorter and 

 lose their cilia, and in the smallest tubules are of a flattened 

 almost squamous type, where finally they appear as if they 

 were directly'' continuous with the germinal epithelium. 



The ripe ova are of an orange or vermilion color, measuring 

 about 50 Ai in diameter, the nucleus is relatively large, the nucle- 

 olus conspicuous, and the cytoplasm crowded with yolk granules. 

 The spermatozoa are small and of the typical shape, with a long 

 flagellum attached to the broad end. 



The blood of Pecten is a slightly cloudy, colorless fluid, it 

 does not coagulate, but when shaken a number of small, white, 

 floccular masses appear, which soon fall to the bottom of the tube 

 leaving the supernatant fluid clear and transparent. These 

 masses consist of blood corpuscles, agglutinated to form Plas- 

 modia. 



The corpuscles although varying in size, are only of one kind. 

 They are amoeboid bodies, which when expanded protrude a 

 number of slender pseudopodia. When contracted, they are 

 ovoid or spherical. There is a single compact nucleus, staining 



