SCIENTIFIC SUMMARY. 
333 
the contractile vesicles are placed one on either side of the largest stomach 
sac. The body has no division between it and a tail-like foot-stalk, and it 
has neither masticatory bulb nor teeth, both of which are present in tube- 
dwelling rotifers. The length of the case is ^th, and of the extended 
animal ~th of an inch. 
The Management of the Fresh-water Aquarium. — Mr. Charles B. Brigham 
has a paper in the American Naturalist for March, describing the mode of 
managing the fresh-water aquarium. For the tank he says that a glass rod 
about a foot in length and a quarter of an inch in thickness will be of use 
in moving the specimens into place when disarranged. Too much cannot 
be said against unnecessarily meddling with the specimens in the aquarium ; 
a slender rod with a sponge attached to the end of it will be useful in 
removing the confervas from the sides of the tank ; a small gauze net three 
or four inches in diameter is often needed to remove dead or objectionable 
specimens ; an india-rubber pipe several feet in length affords the simplest 
method of drawing off the water of the tank ; a fine gauze should be placed 
over that end of the pipe which is in the tank, otherwise the specimens may 
pass through it and be lost. Should the water in the tank become impure 
by any means it can often be purified by the following simple method ; take 
a small earthen flower-pot holding about a pint, and insert a piece of 
sponge tightly in the opening at the base so that when the water is placed 
ih it it will pass through the sponge only drop by drop ; the pot being filled 
with one-third powdered charcoal and two-thirds water, place it over the 
tank and let it empty itself into the aquarium. The effect of this simple 
contrivance is astonishing, and it will often save one the trouble of arranging 
the aquarium anew. 
The Habits of the Aye- Aye. — It is so generally supposed by naturalists 
that Professor Owen’s notion of the evidence of design illustrated by the 
habits of the aye-aye is a mistaken one that the following letter, addressed 
by Mr. Humphry Sandwith to a weekly contemporary, is of especial interest : 
— “ As a simple matter of fact, allow me to state that I kept a living aye-aye 
(now preserved in the British Museum) in a large cage in the Mauritius, and 
as its food I gave it the maggot that infested branches of a species of acacia. 
The animal used to spend its evenings in feeding, as follows. It listened 
attentively at the branches, tapping occasionally the most perforated parts j 
it then tore off pieces of the wood around the maggot-hole, inserting the 
peculiar long finger as a probe from time to time, and ended by extracting 
the maggot by means of this long finger and its strong rodent teeth. I 
have seen the operation scores of times.” 
Animal Life at Great Depths in the Ocean. — Those who wish to read a 
short but well-condensed account of the development of our knowledge of 
this subject will find it in a paper by M. A. J. Malmgren, in Siebold and 
Kolliker’s Zeitschrift, April 1. Beginning with the earlier observations of 
Sars, Koren, Danielssen Loven, and others, it then deals with the labours of 
Edward Forbes, Dr. Wallich, Milne Edwards, and at last brings us down to 
the inquiries of Carpenter, Thomson, and Gwyn Jeflrys. 
The Cornea of the Dee. — In a paper published in the April number of the 
Journal of the Quekett Club Mr. B. T. Lowne gives an excellent description 
of this structure. “ The external layer is far thicker than in the fly, although 
