res under observation. A snail will generally see a black ball at
twelve or fourteen inches; sometimes it will not perceive the ball,
however, until it has been brought to within six or eight inches of its
eyestalks. During the season of courtship snails easily perceive one
another at the distance of eighteen or twenty inches. I have often
watched them at such times, and have been highly entertained by their
actions. The emotional natures of snails, as far as love and affection
are concerned, seem to be highly developed, and they show plainly by
their actions, when courting, the tenderness they feel for each other.
This has been noticed by many observers of high authority, notably
Darwin, Romanes, and Wolff.[11] Mantagazza, a distinguished Italian
scientist, in his _Physiognomy and Expression_, writes as follows: "As
long as I live I shall never see anything equal to the loving tenderness
of two snails, who, having in turn launched their little stone darts (as
in prehistoric times), caress and embrace each other with a grace that
might arouse the envy of the most refined epicurean."[12]

[10] Lubbock, _loc. cit. ante_, p. 140.

[11] Romanes, _Animal Intelligence_, p. 27.

[12] Mantagazza, _loc. cit._, p. 97.

Darwin tells us that two snails, one of them an invalid, the other in
perfect health, lived in the garden of one of his friends. Becoming
dissatisfied with their surroundings, the healthy one went in search of
another home. When it had found it, it returned and assisted its sick
comrade to go thither, evincing toward it, throughout the entire
journey, the utmost tenderness and solicitude.[13] The healthy snail
must have used its sight, as well as its other senses, to some purpose,
for, if my memory serves me correctly, we are told that the sick snail
rapidly regained its health amid its new surroundings.

[13] Darwin, _Descent of Man_, pp. 262, 263.

The crayfish also has its eyes at the tips of eyestalks, but the eyes of
this creature are very different, indeed, from the eyes of the snail.
They are what are known as compound eyes, a type common to the crayfish
and lobster families. Viewed from above, the cornea of a crayfish is
seen to be divided into a number of compartments or cells, and looks, in
this respect, very much like a section of honeycomb. The microscope
shows that in each one of these cell-like compartments there is a
transparent cone-shaped body; this is called the crystalline cone. The