EXPLANATION OF FIG. 1. 



A, Hinge or anteiior nmlional end of the Itjft valvo of an adnlt oyater, npon Tvhioh the soft parts of the animal are represented as they lie i?* 



situ, but with the greater pait of the mantle of the right Bide removed. 

 a u. The auricle of the right side of the 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 suspensiim. 

 Bm. Body-mass, traversed superficially hy the generative ducts g e. 

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



is its connection with the genii. o-uiinary sinus g indicated.) 

 hp. The large branchial pores which open from the subdivided cavities of the pouch-like gillis g into the cloaca cl. 

 br. The anterior branch io cardiac " vein, " which convoys part of the blood from the gills to (he auricle. 



c. Right pericardiac membrane, which bas been thrown back over M in order to expose the heart ve and au. 



c I. Cloaca! 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, which connects the parieto-Rplanchnio with the snpra-cesophageal ganglion. 



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



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



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



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



M. Great adductor muscle, which is here viewxd from the end, and which is attached to the inner facesof the valves over the dark purple scars. 



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

 ■m. Mouth. 



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

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



the palps is called the cuculliis. 

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

 p d. Pedal muscle of light side, which ig also ineerted upon tht; shell of tbe same side. 

 p g, Parieto-splanchnic ganglion. 

 s. Genital opening of the right side. 

 s g. Supiaoeeophageal ganglion. 

 V. Vent or anus. 



V e. Yentricle of the heai-t, which is dilated, or in the condition of diastole. 



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

 the mantle. 



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

 ports the gills. 



EXPLANATION OF FIG. 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 aide, 

 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 large 

 clusters of minute follicles, and part of the course of the intestine t. At^ the widened pyloric part of the intestine is shown, which incloses 

 the crystalline style. The ventricle ne and auricle are much contracted, and a spftcious 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. 



EXl'LANATWN OF FIG. '6. 



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

 ducts d of the "liver " L are bhown cut open longitudinally, and are represented as opening directly into the cavity of the stomach s(, in front 

 of which the cesophagiis oc is also sho^vn running back from the mouth in. This tlgure shows almost the entire intestine, with its widened 

 anterior end^', and its course nnd curvatui'e as liere represented is what will be found constant, even when hundreds of specimens aie exam- 

 ined. Nearly all tJie substance ol the body-mass has been carefully removed from tbe right half of the body, and where the edges of the 

 body have been cut through the stratum of reproductive tissue p e is also shown. The corrugated outer surface of the inner or lower palp 

 at P. The remaining letters have the same eignificunce as in the previous figures. 



EXI'LANATION OF FIG. 4. 



This represents a section or slice out fi-om the soft parts of an oyster at the level of the dotted line o in Pig. 3, and viewed from its 

 anterior surface. The tissues and structures which have been cut across i u this section are as follow s ; 

 a'. The dorsal or posterior branch of the great splaochnie artery. 

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

 h T. Branchial vessels, 

 c. The connective tissue which envelopes the organs contained in the body-mass and forms the princix>al 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 immediately underlies the mantel layer m (. Intestinal canal out through at two points, t i 



posteriorly and anteriorly, shuwiug the manner in which the intestinal walls are folded inwards upon tliemselves. 

 L L. Kight and left lobes of the liver, embedded in the connective tissue and moat considerably developed at the sides and below the 



stomach. 

 8 b. Suprabranchial space. 

 a t. Stomach, showing its irregular foiiu and connection by moans of spacious ducts with the "liver." 



V c. Vena cava. 



7X2 



