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Rotifera, Occasionally the observer is startled by seeing move across the field of his microscope a thing with long stiff outstretched tail, like a mouse; and he can hardly believe that he is looking at a creature only the 120th of an inch long. It bears the expressive name of Monecerea rattus, or Rat-single-tail; the tail being, as already explained, a sort of foot prolonged backwards. This species may be looked for among duck-weed in the earliest days of spring, and all through the summer months. Closely allied to it, if not of the same genus, is Mastigocerea earinata, or Keeled-whip-tail; whose chief distinction is a dorsal expansion of the integument, like a keel. The body is about the 160th of an inch long by about the 400th of an inch broad, inclusive of the keel. It has a crimson eye-spot, and is found among confervoid plants.

I well remember the pleasurable surprise with which I saw for the first time, in the month of May, a fine example of Natanenata tigris, so called from having its eye-spots situated on the back of the neck. It may easily be recognised by its long pair of forceps, or double setæ of the tail-loot, the longer blade being the 140th of an inch in length, nearly twice as long as the body. I noticed numerous transverse lines on the thinner half of each seta, about fourteen on the longer, and eight on the shorter of the two, These quasi-jointings evidently contributed to the flexibility of the organ. The outer cuticle of the body was soft, and allowed the mast varied contortions on the part of the animal, On one occasion, in the month of June, I observed in sore water taken from a small pond in our Arboretum, an egg covered all over with hairs, I watched the egg for some hours in a live-box. The enclosed animal fidgetted about in its narrow prison, and appeared to be rasping the membrane at one end of the egg, The crimson eye-spot was beautifully distinct. At last the shell was broken trough, and the tiny prisoner struggled into freedom. In a few moments it unfolded its limbs from their doubled-up posture, and sailed merrily away, unmistakably a young Scaridium longicauda. As its name, Long-tailed-leaper, implies, the Searidium can leap as well as swim, it leaps with the aid of its tail-foot, which attains the considerable length of the 90th of an inch, the body measuring only the 137th of an inch.

It is a good plan for the microscopist to make drawings for future reference of everything noticeable which he meets with, Referring to my notebook, I find sketches of the ventral and posterior aspect of what I take to be Euchlanis triquetra, although Pritchard fails to notice the lateral fissure between the upper and lower valves. The body-shield, seen from behind, looks like a three-cornered hat. It evidently consists of three valves, two dorsal rising in a ridge along the middle and divided by a deep furrow, and one ventral, separated from the foregoing at the sides. There is also a large opening behind, extending some way on the under surface, and giving liberty to the tail-foot to double up beneath the ventral valve, My first observed specimen happened to lay an egg while under examination. The egg was the 190th of an inch long, the length of the parent’s body being the 80th of an inch. A near relation of Eucldanis is Salpina, a very common object in freshwater gatherings. The lorica is three sided, with a dorsal ridge furrowed from end to end.