XIV.
One fine morning during the month of January, on peering into my largest tank I perceived, attached to the upper portion of the marble arch (centre piece), a peculiar object that had evidently been deposited during the preceding night, but by whom or by what means I knew not. It resembled a fungoid growth, or riband of flesh, plaited up and attached at one edge to the stone. At every undulation of the water the object moved to and fro with an extremely graceful motion.
By careful and close examination it was seen to be covered with a film, that gradually expanded until it burst, and thus gave means of escape to thousands of minute white granules. On submitting these to the microscope, a most wondrous sight met my astonished eyes. Each dot or granule proved to be a transparent shell, resembling the periwinkle or rather the nautilus in shape; containing an animal whose excited and rapid movements were amusing to witness. From out the opening of the shell appeared now and again two rings of cilia. When these organs were about to be put into action, they reminded me of two circular tubes of gas connected together, and each containing innumerable perforations, which were sometimes suddenly and entirely lit up by a torch being applied to one end.
The cilia may be distinctly seen to play at a certain point, and then gradually extend round the circumference of the rings. When the whole are in full action their movements are so extremely swift as to appear devoid of motion, and thus bear a resemblance to rings of flame.
The result of the movements of the cilia was always evident in the vigorous evolutions of the little embryos, for the microscope filaments, while in action, caused the animal to roll about in all directions in a confined circle. When this envelope burst, the little nautiline dashed out, and then—then it was of little use attempting to get a view of the animal again, so rapid and violent were its movements to and fro, never resting for one instant on any spot, and least of all the spot wished. By the aid of blotting-paper, I sometimes reduced the quantity of water in the watch glass; and the animal, thus being compelled to confine its evolutions to a narrower stage, was more often within the field of view.
On visiting the sea-shore shortly after the discovery of the egg cluster just described, I perceived attached to numberless stones and large boulders thick clusters, composed of the self-same objects! Beside them were lying confused heaps of sea-slugs, evidently exhausted with their hatching exertions. Anything more repulsive to the eye than those animal heaps exhibited it would be difficult to conceive. Yet, at the same time, I know of no sight more pleasing than to watch the Doris in its healthy state, gliding along with outspread plume on the under surface of the water, or up the sides of the tank, more especially if it be observed through a powerful hand lens.
These remarks will perhaps convey some new information to the young naturalist, embracing as they do the leading facts connected with the wondrous embryotic development of many marine animals. The reader will already be prepared to learn that the vivacious little animal, moving by aid of cilia and enclosed in a shell, was in reality the youthful stage of that slow creeping gasteropod the Doris, which, in its mature form, is possessed of no cilia, nor any shelly covering whatever.
I should not have introduced this subject so familiarly did I not feel anxious to make my readers aware how easy it is for each of them to conduct experiments in the early stages of embryotic development, and to gain practical evidence of the wonders which this study unfolds.