434 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Plate LXXXVIII— Continued. 

 Yoldia, Venus, Pecten, Ostrea: 



Fig. 67. A few spermatozoa, to show A'ariation in appearance in ditferent forms and in the same 

 individual. "Tails " represented about half length, ft, spermatozoim of Yoldia ; h, of Venus, 

 normal shape ; c, of Venus, a very usual abnormality ; d, of Pecten, normal shape ; e, of Ostrea; 

 f, of Pecten, an abnormal condition. 

 Pecten irradians — Scallop : 



Fig. &^. Mouth fringe on edges of palps. A, bunch of fringe, seen from outer surface of lip ; B, 

 small jiortiou of fringe of lip magnifled, view of inner surface. 

 Yoldia Umatilla: 



Fig. 69. Digestive tract of Yoldia. m, mouth ; s, stomach ; i, intestine ; pa, posterior adductor ; r, 

 rectum. 

 Venus mercenaria — Qiiahog : 



Fig. 70. Cross-section of single fold of gill; ra, reentering angle of fold; fit, filaments; miis, 

 muscle fibers of partition connecting lamelhe of gills; l)v, blood-vessel in partition; jj&.Sf, 

 great blood sin us from j)artition wall, sometimes almost filling half of a water tube of gill; 

 fbs, blood sinus in inner edge of the filament, at the secondary reentering angle of fold. This 

 sometimes becomes, with the one opposite in the other lamella, as large as the partition sinus 

 in the figure, the latter disappearing; mus, muscle fibers at inner edges of filaments. 



Plate LXXXIX. 



Pecten irradians — Scallop : 



Fig. 71. Generative gland; ov, ovary; t, testis; ep, ciliated epithelium on surface of visceral 

 mass; glc, gland cells; 6»i, basement membrane; ct, tissue of irregular cells beneath epithe- 

 lium; /ep, follicular epithelium; d, ciliated ducts, the one in the testis containing sperma- 

 tozoa, and on its walls a gland cell is shown; bv, blood vessel. 

 Ostrea virt/hi iana — Oyster : 



Fig. 72. Hermaphrodite gland; ep, ciliated epithelium of surface of visceral mass; glc, gland 

 cell; fep, follicular epithelium, apparently giving rise only to ova; ov, ovum; some are 

 free, some attached to walls of follicle; sper, apparently ripe spermatozoa completely filling 

 lumen of follicles; spermatozoa and ova occupy same follicles. 

 Venericardia borealis : 



Fig. 73. Section horizontally across byssus organ; fd, folded secreting surface; bs, byssus secre- 

 tion in fold ; bm, muscles of byssus cut transversely ; c, large clear cells near inner edges of 

 folds. 



Fig. 74. Excretory epithelium of one of folds of same, more magnified ; cc, columnar cells over 

 the distal ends of which is a striated layer probably of the byssus secretion, but appearing 

 much like cilia; bs, evident byssus secretiQn; Ic, transparent cells at base of fold, without 

 nuclei, outer edges indistinct and striated ; &t!, blood vessel with endothelial lining. 



Plate XC. 



Pecten irradians — Scallop : 



Fig. 75. Section across mouth fringe; ep, rod-like epithelial cells bearing long cilia; bm, base- 

 ment membrane; glc, large, elongated gland cells, the nuclei of some being visible; bi\ blood 

 vessel with endothelial lining. 



Ostrea virginiana — Oyster: 



Fig. 76. Transverse section of gill ; 1, 2, 3, 4, folds of lamella between two lamellar partitions;/,, 

 ciliated frontal epithelium of filament of fold; fi, ciliated epithelium of frontal region of 

 modified filament, at reentering angle of fold; chi, chitinous rods in filament of fold; c/m, 

 chitinous rods of modified filament; ?•«, reentering angle of fold; Z/, cilia of cells of strain- 

 ing line; gle, gland cells; mus, muscle fibers; J7c, spherical cells in partition connecting gill 

 lamellse; wt, water tube; be, blood corpuscles; 6r, blood vessel of partition ; cjj, epithelium 

 of partition ; //, filament, transitional between filament of fold and filament of reentering 

 angle. 



