230 THE WORLD OF THE SEA. 
egg; of course there is no calcareous shell, but the whole is encased 
in a film. Ina few days the yolk becomes an embryo, which gives 
evident tokens of life by continuously turning round; this motion is 
soon extended to the sides of the envelope, so that the embryo 
moves from side to side of the egg, in an ellipse. This movement 
is produced by a number of extremely minute vibratory cils, which 
are placed irregularly, and hence they cause a spinning motion. 
These cils take the place of all the other organs which are as yet 
undeveloped in the minute creature. They absorb the air and the 
nourishment necessary for its growth. To fulfil these two functions 
motion is necessary; it is indispensable that there should exist 
regular currents, by which the required air and food comes in 
contact with the young mollusk. As the growth continues the cils 
gradually disappear, and consequently the motion gradually 
decreases. From their birth no cils had ever appeared upon the 
places beneath which any organs were in an undeveloped state ; 
and this accounts for the manner in which the cils are irregularly 
distributed. During the time that the rotatory motion was in pro- 
gress the development of the mollusk proceeded. As its soft body 
lengthened, it became twisted like a corkscrew; and since the animal 
turned upon itself a little obliquely, the body partook also of that 
characteristic. The firm parts of the body—that is, the foot, the 
head, and the tail—being too stiff to be affected by the motion, 
are, therefore, not twisted. The shell, which forms itself slowly, is 
moulded to this twisted body, and consequently partakes of the 
spiral form. Spiral shells may be considered as calcareous tubes, 
which gradually increase from the apex to the base, and whose 
walls are rolled upon themselves after various fashions. ~The real 
or ideal axis about which the revolution is made has been called 
the column. When the column is hollow, its lower opening is the 
umbellicum. The spiral of the univalves nearly always turns from 
right to left. Charles Bonnet long ago remarked this. If it be 
asked why this should be the direction of the rotation, we can 
only answer, that it seems to be a great law of nature that all 
rotation should be from right to left. The sun, the planets, and 
the earth, are all subservient to this law. | 
Men rather use their right hands than their left. If the 
vertebral column deviates, it is on the right side. Our staircases, 
