Anatomy of the Snail (Helix pomatia.)

Fig. 264. Anatomy of the Snail (Helix pomatia).

(1389). An organ, named by Swammerdam the "sacculus calcareus," has recently been supposed by Mr. Jacobson to perform the office of a kidney. "Chemical analysis of the matter secreted by this viscus has led him to discover in it uric acid, ammonia, or calcareous salt, and water. He was unable to discover any trace of uric acid in any other part of the animal; and as, in the superior animals, the kidneys are the only organs which, in a state of health, secrete uric acid, and as the calcareous sac of the Snails has many other anatomical relations with the kidneys, Mr. Jacobson concludes that this sac represents the kidneys, and must be so considered in all the Mollusca which are provided with it*".

(1390). Before we enter upon a description of the somewhat complex generative system of a Snail, it will be proper to advert to one or two remarkable circumstances connected with the procreation of these singular animals. We must first premise that every individual is hermaphrodite, and moreover presents a kind of hermaphroditism of the most perfect and complete description, possessing elaborately-constructed male and female organs, which are distinct and separate from each other; but, nevertheless, the cooperation of two individuals is essential to the mutual impregnation of both. The manner in which they copulate is not a little curious, their union being accompanied by preparatory olandishments of a very extraordinary kind, that to a spectator would seem rather like a combat between mortal foes than the tender advances of two lovers. After sundry caresses between the parties, during which they exhibit an animation quite foreign to them at other times, one of the snails unfolds from the right side of its neck, where the generative orifice is situated, a wide sacculus, which, by becoming everted, displays a sharp dagger-like spiculum or dart attached to its walls.

Having bared this singular weapon, it endeavours, if possible, to strike it into some exposed part of the body of its paramour, who, on the other hand, uses every precaution to avoid the blow, by speedily retreating into its shell. But, at length having received the love-inspiring wound, the smitten snail prepares to retaliate, and in turn uses every effort to puncture its assailant in a similar manner. The darts are generally broken off in this encounter, and either fall to the ground, or else remain fixed in the wounds they have inflicted. After these preparatory stimulations, the snails proceed to more effective advances. The sac of the dart is withdrawn into the body, and another sacculus is by a like process protruded from the common generative aperture. Upon the last-named organ two orifices are seen, one of which leads to the female generative system, while from the other a long and whip-like penis is slowly unfolded, being gradually everted like the finger of a glove, until it attains the length of an inch or more; and then each of the two snails, by inserting its penis into the female aperture of the other, impregnates its partner, and is itself impregnated at the same time. Such is the peculiar manner in which the amours of snails are conducted.

Let us now examine the internal viscera connected with the process.

(1391). The sac of the dart first requires our attention. This viscus, when uninverted (for it must be turned inside out in order to expose the weapon within it), is a thick muscular bag (fig. 264, a'); and on opening it, it is found to contain the dart, attached to a nipple-like protuberance at the bottom of the sac. The dart itself is four-sided; and as it grows by the constant addition of calcareous particles deposited at its base from the surface of the vascular protuberance to which it is fixed, so, if broken off, it is speedily reproduced in a similar manner.

* Edinb. Journ. of Nat. and Geogr. Science, iii. p. 325.

(1392). The male part of the generative system is composed of a testicle, vas deferens, and the whip-like penis above described.

(1393). The testicle is considered by Cuvier* to consist of two distinct portions: one, a soft whitish oval mass (fig. 264, p); while the other is elongated, thin, and granular (y), being imbedded among the convolutions of the oviduct (w.) The vas deferens forms the excretory duct of both these portions, and terminates in the side of the penis, its orifice becoming, of course, external when that organ is protruded by evolution. The intromittent organ itself, as seen when lodged within the body of the snail, consists of two parts, a muscular bag which forms its body (b'), and a long whip-like portion (z); the latter is hollow, but not perforated. The reader will now have little difficulty in understanding how this remarkable apparatus is protruded. The generative sac, common to both the male and female organs, first becomes inverted; the body of the penis (b') then undergoes inversion in a similar manner, so that the orifice of the vas deferens appears externally; and lastly, the long appendage to the penis (z), being likewise turned inside out by the action of the muscles that compose its walls, completes this strangely-constructed instrument.

Its subsequent retraction into the visceral cavity is effected partly by the assistance of a special retractor muscle, which acts upon the body of the penis, but principally by the same contractility that accomplished its evolution.

(1394). The female system next demands our notice; and this will be found to present for our investigation an ovary and lengthy oviduct, to which are appended certain auxiliary organs, namely the spermatheca and the multifid vesicles.

(1395). The ovary (fig. 264, s) is found situated in the inmost recesses of the shell, and partially imbedded in the substance of one of the lobes of the liver. From the ovary a long oviduct (q) is derived, which is at first thin and slender, but, soon becoming wider and more capacious (u), it gradually expands into an extremely convoluted intestiniform viscus, to which the name of uterus has been improperly given, and ultimately terminates in a canal derived from the spermatheca, to be described hereafter. It is during their passage through this enormous oviduct that the eggs attain their full growth preparatory to their expulsion from the body.