128 
THE YOUNG SCIENTIST. 
though slow, evince a decided purpose 
and ability to make all parts work to- 
gether for one common object; and as 
might be expected from this fact, and also 
from the repetition of distinct, although 
not articulated limbs, they are provided 
with a nervous apparatus of considerable 
development, in the shape of a chain of a 
ganglia and a brain, with connecting fila- 
ments. From these and other circum- 
stances naturalists consider the Tardi- 
_grada to belong to the great family of 
Spiders, of which they are, physiologic- 
ally speaking, poor relations. Siebold 
says " they form the transition from the 
Arachnoidse to the Annelides."* Like 
tlie spiders they cast their skin ; and, al- 
though I Avas not fortunate enough to 
witness this operation — called in the 
language of the learned ecdijsis, which 
means putting its clothes off— I found an 
empty hide, which, making allowance for 
the comparative size of the creatures, 
looked tough and strong as that of a 
rhinoceros, and showed that the stripping 
process extended to the tips of the claws. 
The ' Micrographic Dictionary' states 
that the Tardigrada lay but few eggs at a 
time, and these are "usually deposited 
during the ecdysis, the exuviae serving as 
a protection to them during the process 
of hatching." Thus Mrs. Water-Bear 
makes a nursery out of her old skin, a 
device as ingenious as unexpected. The 
water-bears are said to be hermaphrodites, 
but this is improbable. 
The Plumatella repens, described in a 
former chapter, was kept in a glass 
trough, to which some fresh water was 
added every few days, taken from a glass 
jar that had been standing' many weeks 
with growing anacharis in it. One day a 
singular creature rnade its apjDearance in 
the trough ; when magnifled sixty dia- 
meters it resembled an oval bladder, with 
a sort of proboscis attached to it. At one 
])art it was longitudinally constricted, 
and evidently i)ossessed some branched 
and complicated internal vessel. The sur- 
face was ciliated, and the neck or pro- 
boscis acted as a rudder, and enabled the 
creature to execute rapid turns. It swam 
up and down, and round about, some- 
times rotating on its axis, at others keep- 
ing the same side upjiermost, but did not 
exhibit the faintest sign of intelligence in 
its movements, except an occasional 
finger-like bend of tlie proboscis, upon 
which the cilia seemed thicker than upon 
the body. It was big enough to be ob- 
served as a moving white speck by the 
naked eye, w^hen the vessel containing it 
was held to catch the light slantingly; 
but a power of one hundred and five was 
conveniently employed to enable its 
* 'Anatomy of the Invertebi-ata,' Burnett's 
trans., p, 364. 
structure to be discernei. Under this 
power, when the animal was resting or 
moving slowly, a moutn Avas perceived on 
the left side of the proboscis, which was 
usually, though not always, curved to the 
right. The mouth was a round or oval 
orifice, and when illuminated by the 
parabola, its lips or margin looked thick- 
ened, and of a pale blue, and ciliated, 
while the rest of the body assumed a 
pinkish i)early tint. 
Below the mouth came a funnel-shaped 
tube or oesophagus, having some folds or 
plaits on its sides, and terminating in a 
broad digestive tube, distinct from the 
nucleus, and ramifying like a tree. The 
constriction before mentioned, which was 
always seen in certain positions, although 
it varied very considerably in depth and 
width, drew up the integument towards 
the main trunk of the digestive tube, and 
thus the animal had a distinct ventral and 
dorsal side. The branches of the tube 
stopped somewhat abruptly just before 
reaching the surface, and were often ob- 
served to end in small round vacuoles or 
vesicles. 
At the bottom of the bladder, opposite 
the mouth, in some specimens were large 
round cavities or cells, filled with smaller 
cells, or partially transparent granules. 
These varied in number from one to two 
or three, and were replaced in other 
specimens by masses that did not present 
the same regular form or rounded out- 
line. In one instance an amorphous 
structure of this kind gradually divided 
itself, and seemed in the course of forming 
two cells, but the end of the process was 
unfortunately not seen. The annexed 
Trachelius ovum (slightly flattened). X 105. 
drawing will readily enable the animal to 
be recognized. It shows the mouth very 
plainly, and a current of small particles 
