THE YOUNG 
Marvels of Pond Life.-XY. 
THE creatures described in the preced- 
ing articles range from very simple to 
highly complicated forms, and in describ- 
ing them some attention has been paid 
to the general principles of classitication. 
The step is a wide one from the little 
masses of living jelly that constitute 
Amoebae to the Rotifers, supplied with 
organs of sensation — eyes, feelers (cal- 
cars), and the long cilia in the Eloscu- 
larians which seem to convey impression 
like the whiskers of a cat — together with 
elaborate machinery for catching, grind- 
ing up, and digesting their prey, and 
which are also well furnished with respir- 
atory and excretory apparatus, ovaries, 
etc. In the polypi and polyzoa may be 
observed those resemblances in ax^pear- 
ance which induced early naturalists to 
group them together, and also the wide 
difference of organization which marks 
the higher rank to wliich the latter have 
attained. Amongst the ciliated infusoria 
important gradations and differences will 
also be noticed, some having only one 
sort of cilia, others two sorts, and others, 
again, supplied, in addition to cilia, with 
hooks and styles. No perfectly satisfac- 
tory classification of the infusoria has yet 
been devised, and the life history of a 
great many is still very imperfectly 
known. On the whole, the tendency of 
research is to ])lace many of tliem higher 
than they used to stand after Ehrenberg's 
supposition of their having a plurality of 
distinct stomachs, etc., was given up. 
Balbiani and others have sliown numer- 
ous cases of their forming their eggs by 
a process analogous to that of higher 
animals. Some really are, and others 
closely resemble, the larval conditions of 
creatures higher in the scale, and the con- 
tracted vesicle with its channel bears re- 
semblance to what is called the "water 
vascular system ' of worms. 
Zoological classification depends very 
much on morphology, that is, the tracing 
of particular structures, or parts, through 
all their stages, from the lowest to the 
highest forms in which they are exhibited. 
In this way the swimming bladder, of a 
fish is shown to be a rudimentary lung, 
though it has no respiratory functions, 
and Mr. Kitchen Parker has found in the 
imperfect skull of the tadpole a rudimen- 
tary appearance of bones belonging to 
the human ear. The comparative anato- 
mist, after a wide survey of the objects 
before him, arranges them in groups! He 
asks what are the characteristic things to 
be affirmed concerning all the A's that 
cannot be said of all the B's ; or of all the 
C's that marks their difference from the 
A's or the D's. Careful investigation 
upon these methods shows affinities 
where they were not previously expected — 
SCIENTIST. 139 
birds and reptiles being close relations, for 
example, instead of distant connections — 
and they lessen the value for purposes of 
classitication of peculiarities that might 
have been of the highest importance. 
Professor Huxley divides the verte- 
brates into Ithycoids, comprising tishes 
and amphibia, which besides other char- 
acteristics, have gills at some period of 
their existence; Sauroids (reptiles and 
birds), which have no gills, and possess 
certain develo|)mental characteristics in 
common ; and, lastly, Mammals. The In- 
secta, Myriopoda, Arachnidae, and Crus- 
tacea, he remarks, " without doubt pre- 
sent so many characters in common as to 
form a very natural assemblage. All are 
provided with* artiticial limbs attached to 
a segmented body skeleton, the latter, 
like the skeleton of the limbs, being an 
' exoskeleton,' or a bordering of that layer 
which corresponds with the outer part of 
the vertebrates. In others, at any rate in 
the embryonic condition, the nervous 
system is composed of a double chain of 
ganglia, united by longitudinal commis- 
sures, and the gullet passed between two 
of these commissures. No one of the 
members of these four classes is known 
to possess vibratile cilia. The great 
majority of these animals have a distinct 
heart, provided with valvular apertures, 
wtiich are in communication with a peri- 
visceral cavity containing corpusculated 
blood. ' These four classes have con- 
stituted the larger group or *' province " 
of Articjilata or Arthropoda. Professor 
Huxley thinks that, notwithstanding " the 
marked differences " between the Anne- 
lida (worms) and the preceding Arthro- 
pods (joints -foots), their resemblances 
outweighing them— the characters of 
the nervous system, and the frequently 
segmented body, with imperfect lateral 
appendages of the Annelida necessitates 
their assemblage with the Arthropoda in 
one great division, or sub-kingdom, of 
Annulosa. 
Tracing analogies between Echinoder- 
raata (sea urchins, star-flsh, etc.) and the 
Scolecida (intestinal worms), he places 
them together as AnniiJoida. 
Cephalojioda, Pteropoda, Pulmo-gaster- 
opoda, and Branchio-gasteropoda, having 
resemblances of nervous system, and 
"all possessing that remarkable buc- 
cal apparatus, the Odontophore," are 
l^laced together by him as Odontophora. 
The Odontophores (tooth-bearers) are 
familiar to microscopists as the so- 
called palates of mollusca. Placing with 
the above the lamellibranchial mollusks 
(mollusks with gills formed of lamellae 
or little plates'), Ascidioida (ascidians,) 
Brachiopoda (larnpsheds), and Polyzoa,. 
in s]ite of their differences, he forms an- 
other great group, Annuloida. 
