SPONTANEOUS FISSION IN AN AQUATIC WORM. 275 
intestine in some of the groups, to which in others a crop and 
gizzard are added. There are also small tortuous tubes floating 
in the perivisceral space, with enlarged circular terminations or 
orifices in nearly all the segments ; they are supposed to have an 
excretory function. It is unnecessary here to notice other anato- 
mical peculiarities, except that, when mature, both sexes are found 
in the anterior segments of,the same individual. The sense of sight 
is present in some of the group. 
The order was divided by Claparéde into two families: the Ze7- 
ricola, or earth-worms, and the Zzmzcola, or mud and water-worms. 
D’Udekem, however, divided them according to their modes of 
reproduction, into gemmiparous and non-gemmiparous. The former 
are water-worms, and are able to swim and pursue their prey; the 
latter are unable to do so, and inhabit moist earth or mud. A 
sub-family of the Limicolee are the Naididze, or nymph-worms, re- 
markable for their transparency and the freedom of their motions, 
but chiefly by their power of reproduction by budding and fission. 
They are hermaphrodite, but the sexual elements are not developed 
until they approach maturity. Previous to the attainment of this 
condition, however, they are said to multiply by self-division. 
Charles Bonnet, an eminent Swiss naturalist, who lived in the 
latter half of the last century, was the first to describe the self 
division of worms, and to experiment upon their powers of repro- 
duction. Prof. Owen says that “ Bonnet progressively increased 
the number of sections in healthy individuals of a small worm, 
Lumbricus variegatus, and when one of these had been divided 
into twenty-six parts, almost all of them reproduced a head and tail, 
and became so many new and perfect individuals.” ‘‘ Bonnet cut 
off the head of one of these worms, and as soon as a new head 
was completed he repeated the act; after the eighth decapitation, 
the unhappy subject was released by death; the execution took 
effect, the reproductive virtue had been worn out.” Again, “‘ With 
this power of reproduction of lost extremities, is associated that of 
spontaneous fission in the genus /Vazs. In this little red-blooded 
worm the last joint of the body gradually extends and increases to 
the rest of the animal; its anterior part begins to thicken, and to 
be marked off by a deeper constriction from the penultimate link. 
In the Wats proboscidea a proboscis shoots out from it, like that on 
the head, and it is then detached from the old JVazs. It often 
shoots out, previous to its separation, another young one from its 
own lost joint in a similar way, and three generations of Naids 
may thus be organically connected, and forming one compound 
individual.” 
Dr. Thomas Williams thus characterises these statements :—“ On 
the authority of hundreds of observations, laboriously repeated at 
every season of the year, the author of this report can declare, 
