434 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Plate LXXXVIII— Continued. 
Yoldia, Venus, Pecten, Ostrea: 
Fig. 67. A few spermatozoa, to show variation in appearance in different forms and in the same 
individual. 1 ‘ Tails ” represented about half length, a, spermatozoon of Yoldia ; b, 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. 68. Mouth fringe on edges of palps. A, bunch of fringe, seen from outer surface of lip ; B, 
small portion of fringe of lip magnified, view of inner surface. 
Yoldia limatula : 
Fig. 69. Digestive tract of Yoldia. m, mouth ; s, stomach ; i, intestine ; pa, posterior adductor ; r, 
rectum. 
Venus mercenaria — Quahog : 
Fig. 70. Cross-section of single fold of gill; ra, reentering angle of fold; fil, filaments; mus, 
muscle fibers of partition connecting lamellae of gills; bv, blood-vessel in partition; pbs, 
great blood sin us from partition 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 ; 6m, basement membrane ; ct, tissue of irregular cells beneath epithe- 
lium; fep, 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 virginiana — 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; 6s, byssus secre- 
tion in fold; 6m, 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 ; 6s, evident byssus secretion ; Ic, transparent cells at base of fold, without 
nuclei, outer edges indistinct and striated ; bv, blood vessel with endothelial lining. 
Plate XC. 
Pecten irradians — Scallop : 
Fig. 75. Section across mouth fringe; ep, rod-like epithelial cells bearing long cilia; 6m, base- 
ment membrane; glc, large, elongated gland cells, the nuclei of some being visible ; bv, 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; />, ciliated epithelium of frontal region of 
modified filament, at reentering- angle of fold; chi, chitinous rods in filament of fold; clii, 
chitinous rods of modified filament ; ra, reentering angle of fold; Ifl, cilia of cells of strain- 
ingline; glc, gland cells; mus, muscle fibers; pc, spherical cells in partition connecting gill 
lamellse; wt, water tube; be, blood corpuscles; bv, blood vessel of partition ; ep, epithelium 
of partition ; tf, filament, transitional between filament of fold and filament of reentering 
angle. 
