If a good number of these animals be collected they will probably breed, and then there will be the opportunity of seeing for ourselves the young carried about in the incubatory pouch.
There are two other aquatic I´sopods which will make good subjects for us on account of their great abundance, and the ease with which they may be kept in any improvised aquarium, with a little weed. They may both be taken in brackish water, and will live and thrive in fresh water, without any admixture of salt. Indeed, both have lived for some months in a small bottle of New River water, in which the only weed is some willow moss. They feed on this and on the vegetable débris that accumulates at the bottom of the bottle, and both species have bred.
The first is Idot´ea (I. pelag´ica), a long, narrow creature, with very short inner antennae. The last four segments of the pleon form a plate on the upper surface; and on the under surface the opercular plates may be opened like tiny folding-doors, to show the breathing plates.
These vary greatly in colour. Of another species, Spence, Bate, and Westwood say: ‘According to our experience the colour of the animal is dependent upon that of the weed on which it lives. Those that live on the black fucus are generally very dark purple, while those that we find on the green algae are brightly verdant; and it has always been our opinion that this change was due to the food[55].’
The other little creature is called Sphaero´ma—it has no English name—from the fact that it can roll itself into a ball. It is not difficult to identify, from the fact that all the segments of the pleon are joined into one plate, the hinder margin of which is entire, thus
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The garden will afford us a hunting-ground for the last specimen of this group for which we have space—the Woodlice. Enough has been said of the method of looking over and breaking-up I´sopods generally to render detailed description unnecessary. The inner pair of antennae, however, are so small as to be readily overlooked: indeed, on first sight these creatures seem to have but a single pair. Some have, and others have not, the power of rolling themselves into a ball; and, concerning the former, Swammerdam tells the following story:—
‘One of our maidservants had at one time found a great number of Woodlice in the garden, contracted into round balls ..., and thinking she had found a kind of coral beads, she began to put them one after another on a thread, but it soon happened that these little creatures, which roll themselves up in such a manner only for fear of harm, and appear as if they were dead, being obliged to throw off their mask, resumed their motions. On seeing which, the maidservant was so greatly astonished, that she threw away the Woodlice and the thread, and cried out, and ran away[56].’