PLiVTE 359. 



EXPLAJ^^ATION OF FIO. 1. 



A. Hloge or anterior urobonal end of tho loft valvo of an adult oyator, upon which the soft parts of the animal are represented as they lie t7i 



situ, but with the greater part of the mantle of tho right aide removed. 

 a u. Tho auricle of tho li^ht side of tho heart contracted. 



B. Posterior or ventral end of the left valve, which in life is usually directed upward more or less, and during the act of feeding and respira- 



tion is separated slightly from the margin of its fellow of the opposite side to admit the water needful for respiration, and which 



also contains the animal's food in suspension. 

 Bm. Body-mass, traversed superticially by the generative ducts g e. 

 bj. The organ of Eojanus, or "renal " organ, of tho right side of the oyster. (The ducts wliich it sends into the mantle are not shown, nor 



is its connection with the genito-urinary stuns s indicated.) 

 bp. The large branchial pores which open from the subdivided cavities of the pouch-like gills g into the cloaca rf. 

 br. The anterior branchiocardiac " veiu," which conveys part of the blood ft'om the gills to the auricle. ' 



c. Right pericardiac membrano, which has been thrown back over M in order to expose the heiirt ve and au. 



c I. Cloacal space, through which the water used in respiration passes out, and into which the excrement of the animal is discharged from 

 the vent v. 



d. Nervous commissure of the right side, wliich connects the parieto-splanchnic with the supra-cesophageal ganglion. 



g. Gills, which extend as four flattened transversely, subdivided sacks from the palps p to the jioint y, at the edge of the mantel. 



g e. Superficial uet-work of the generative ducts as they appear when the oyster is spawning. 



h. Groove in the hinae end of the left valve, which receives the ridge developed in the corresponding situation on the right one. 



l. Dark brown elastic body or ligament by which the valves are held together at the hinge. 



M. Great adductor muscle, which is here viewed from tho end, and whicli ia attached to the inner faces of the valves over the dark purple soars. 



It opposes the elastic ligament and closes the valves, and corresponds to the posterior adductor muscle of dimyary mollusks. 

 m. Honth. 



m t. Mantle of the left side fringed with two rows of tentacles ; m V, portion of the mantel of the right side. 

 n to 2 marks the extent to which the right and left loaves of the mantle are joined together; the hood thus formed above and at the sides of 



the palps ia called the cucullns. 

 P. Palps exposed, a part of the cucullus on the right being cut away. 

 p d. Pedal muscle of right side, which is also inserted upon the shell of the same side. 

 p g. Parieto-splanchnic ganglion. 

 8. G«nital opening of the right side. 

 8 g. Supraoesophageal ganglion. 

 V. "Vent or anus. 



V e. Ventricle of the heart, which is dilated, or in the condition of diastole. 



xxz. Areas at the edge of tho inner surface of the shell, where intruded mud has been inclosed by a thin laminee of shelly matter deposited by 

 the mantle. 



y. Point at the posterior extremity of the gills, where the right and left leaves of the mantle are joined together by the membrane which sup- 

 ports the gills. 



EXPLANATION OF FIO. 2. 



This figure was drawn from a dissection of a hardened specimen which'had been removed from the shell, and is viewed from the left side, 

 the superficial tissues of the left half of the body-mass having been removed in order to display the surface of the "liver" L, with its largo 

 clusters of minute follicles, and part of the course of the intestine i. Atj the widened pyloric part of the intestine is shown, which incloses 

 the crystalline style. The ventricle vc and auricle are much contracted, and a spacious pericardiac space is shown on either side of it, g e. 

 Stratum of reproductive follicles. The remaining letters of reference are the same as in Fig. 1. 



EXPLANATION OF FIG, 3- 



This figure of the viscera of the oyster is also drawn in part from the hardened soft parts, but is viewed from the right side. The great 

 duels d of the "liver" L are bhowncut open longitudinally, and are representt^d as opening dii'ectly into the cavity of the stomach «(, in front 

 of which the (esophagus oe is also shown running back from the mouth m. This figure shows almost the entire intestine, with its widened 

 anterior eudj, and its course and curvature as here represented is what will bo found constant, even when hundreds of specimens are exam- 

 ined. Nearly all the substance ol the body-mass has been carefully removed from the right half of the body, and whei"6 the edges of the 

 body have been cut through the stratum of reproductive tissue i? « is also shown. The corragated outer surface of tho inner or lower palp 

 at P. The remaining lettors have tho same significance as in the previons figures. 



EXPLANATION OF FJQ. 4. 



This represents a sectioa or slice cut from the soft parts of au oystsr at the level of the dotted lino o iu Fig. 3, and viewed from its 

 anterior surface. Tho tissues and structures which have been cut across in this section are as follows: 

 a'. The dorsal or posterior branch of tho groat splanchnic artery. 

 a". The anterior or ventral branch of the splanchuic artery. 

 b r. Branchial vessels, 

 c. The connective tissue which envelopes the organs contained in tho body^mass and. forms the principal portion of the substance of the 



animal in winter. 

 g. The gills cut across, showing their hollow interiors. 

 g e. Stratum of reproductive follicles, which inimediatoly upderlics tho mantel layer mt. Intestinal canal cut through at two points, ii 



posteriorly and anteriorly, showing the manner in which the intestinal walls are folded inwai*ds upon themselves. 

 L L. Hight and left lobes of the liver, embedded iu the connective tissue and most considerably developed at the sides and below th« 



stomach. 

 B b. Snprabr&nchial epaoe. 

 « t. Stomach, showing its irregular form and oouuectiou by moans of spacious ducts with tho "liver." 



V c. Vena cava. 



712 



