90 
THE YOUNG SCIENTIST. 
gnats, and other insects, rotifers, includ- 
ing the tubicolar sorts, and several varie- 
ties of infusoria may be expected and 
generally found. There is, however, a 
curious fact about ponds, big and little, 
which Pritcliard remarks upon in his ' In- 
fusoria,' and which corresponds with our 
own experience, that those which have 
proved to be well stocked with any parti- 
cular creature during one year, will very 
likely contain none of it in the next. 
There are of course exceptions to this rule, 
but we have often been astonished and 
disappointed at finding the complete 
change, both in populousness and poi:)ul- 
ation, that a revolution of twelve months 
will make ; and it would be extremely in- 
teresting to notice the changes that took 
place during a term of years. 
Such researches might unfold some un- 
expected laws in the succession of in- 
fusorial life. Those germs which are most 
widely diffused, will be the most likely to 
be developed in any mass of convenient 
water; but how and Wliy the rarer forms 
come and go is very imperfectly under- 
stood. Slight modifications in surround- 
ing circumstances will materially affect 
the result. Thus, if we bring home a 
handful of conferva, and a few water- 
plants of higher organization, such as 
duck-weed and anacharis, and place the 
whole in a glass jar full of pond water, 
we shall at first have a good stock of ob- 
jects ; but they will usually grow less and 
less, luitil scarcely anything is left. If, 
however, we introduce a few pieces of 
straw, or a tiny wisp of hay, we shall suc- 
ceed much better, and not only preserve 
our population longer, but enjoy a suc- 
cession of animated crops. Extensive de- 
composition of vegetable matter kills off 
all but certain families, such as Para- 
mecia, avIio enjoy it ; on the other hand, 
too little decomposition proves fatal to 
some creatures, by depriving them of their 
food, and when tliey have died off, those 
who depended upon them for a living, die 
too. Different vegetables in decomposi- 
tion suit different creatures, and hay and 
straw in that state seem to please the 
largest number. An animalcule tank will 
succeed best Avlien it contains two or three 
kinds of growing plants, which oxygenize 
the air, and a moderate variety of decom- 
posing organisms will supply food with- 
out making the water offensive. 
From these considerations it will be 
apparent that not only the nature of the 
vegetation of a pond, which is often 
changed by accidental circumstances, but 
also tlie quality of the odds and ends that 
the winds may blow into it, or which may 
fall through the air, will do much to 
determine the character and number of 
its inhabitants, while the quantity of 
shade or sunsliine it enjoys, will also 
exercise an important influence. Hay and 
other infusions have from the beginning 
of microscopic investigations been em- 
ployed to obtain the creatures which the 
Germans call " Infusions thierchen " (in- 
fusion animalcules), and the English 
" Infusoria ; " but very little has yet been 
done in the way of their scientific culture 
and management. 
To return from this digression to our 
little Hanipstead ponds, we obtained from 
one, in September, that was full of star- 
weed, a number of sugar-loaf bodies, ad- 
hering to one another, and of a pale yel- 
low brown color. The specimens first ex- 
amined looked complete in themselves, 
and were taken for eggs of some water 
creature. Further search, however, dis- 
closed aggregations of similar sugar- 
loaves that had evidently formed part of a 
tubular structure, and the idea at once 
occurred that they were fragments of a 
Melicerta tube, a conclusion that was 
verified by finding some tubes entire and 
a dead Melicerta in the rubbish at the 
bottom. All the specimens of Melicerta 
tubes w^e had hitherto examined were com- 
posed of rounded pellets, but these were 
made of pointed cones or sugar-loaves, 
with the points projecting outwards from 
the general surface. In Pritchard's ' In- 
fusoria,' these pellets are described "as 
small lenticular bodies," The 'Micro- 
graphic Dictionary ' states that the tubes 
of tlie Melicerta are composed of " numer- 
ous rounded or discoidal bodies;" and 
Mr. Gosse, in his 'Tenby,' which con- 
tains an admirable description, and an 
exquisite drawing of this interesting 
rotifer, calls the pellets " round." 
Not being able to obtain a -living 
specimen of the Melicerta, who made her 
tube of long sugar-loaves, I could not tell 
whether she differed in structure from the 
usual pattern of her race, but the general 
appearance of the dead body was the 
same. It is possible that these creatures 
possest some j^ower of modifying the form 
of their singular bricks, or the^^ may at 
different ages vary the patterns, which 
matters some fortunate i)ossessor of a 
colony of these animals may be able to 
verify. 
In the sediment of the water containing 
the Melicerta cases was found an animal- 
cule about 1-120" long, covered with cilia, 
and having a proboscis seldom more than 
a quarter of the length assumed by the 
body, w^hich continually changed its form, 
sometimes elongating, sometimes shorten- 
ing, and often contracting one side into a 
deep fissure. It was, probably, an Amphi- 
leptns, though not precisely agreeing with 
any drawing or description I am ac^ 
quainted with. Another inmate of the 
same water was a lively long-tailed rotifer, 
with a small oval body, a tuft of vibrating 
cilia and a curved bristle visible among 
them on one side. This creature had a 
