If we now take our dissecting microscope and place an Asellus in some water in an excavated 3 in. by 1 in. slip on the stage, examination with an inch lens will show us a considerable amount of detail. With the half-inch Leitz lens (see p. 18) one may see quite clearly the beautifully annulated form of the flagella of the antennae, the sensory hairs with which these organs are set, and the circulation of the blood in the limbs and the antennae--the corpuscles moving in a continuous stream. More than this: we shall be able with the same power to distinguish tufts of Vorticellids that settle on the Asellus, and the commensal rotifers that roam about on the body of their host, generally on the limbs and under surface. Now we may turn the Asellus on its back, to examine the breathing apparatus more closely than we were able to do when the creature was moving about in the bottle. It will be easy to make out the opercular plates--modified tail appendages--that open and shut to admit water to, or allow it to flow out from, the true breathing-plates which function as gills, and correspond to the swimming feet of the Amphipods. In the female there is a pouch beneath the perei´on, in which the eggs are carried till they are hatched, and which serves as a nursery and refuge for the young. 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].’