370 THE FRESH-WATER SPONGE. 
To an ordinary eye, that any creature should crawl, would not appear a very surprising 
fact, but to the mind of a naturalist, the whole phenomenon is full of wonder. It is easy 
enough for a single being to advance in a given direction, and even though it has a very army 
of legs, like a centipede or a julus, the limbs are all directed by the same mind. But in the 
present case, there is no common centre to which the wills of the myriad polypes that compose 
the group can be referred ; and the locomotive capacities of the Cristatella remain one of the 
many unsolved mysteries with which nature abounds, 
In all respects, this is a remarkable species. Instead of hiding in darkness and coveting 
the shade, as is the case with nearly all the polyzoa, the Cristatella exults in light, and loves 
to crawl in shallow waters where it is exposed to the full blaze of the meridian sun. The 
ordinary length of the Cristatella is from one to two inches, and its general aspect reminds 
the observer of a yellowish-brown hairy caterpillar, softer than the well-known woolly bear, or 
larva of the tiger-moth, and indeed looking much as if it were made from the soft silken 
substance denominated ‘‘ chenille.’ 
It is one of the fresh-water species, and the plume of tentacles is not funnel-shaped, but 
formed as if set in a horseshoe. 
A most marvellous production, which requires some explanation, is the so-called. ‘* stato- 
blast.” It isa rather formidable object. The statoblasts are developed within the cavity of 
the parent, where they may be seen of different sizes, and in most cases arranged like beads on 
a string. They consist of two nearly hemispherical or oval dises, which are united at their 
edges, and the line of junction strengthened by a more or less deep ring, so that the general 
aspect of the statoblast is not unlike that of the planet Saturn. 
In the Cristatella and another genus, the Pectinatella, the statoblast is armed with a 
double series of hooks, starting from the edges of the discs, those of the opposite discs 
alternating with each other and extending well beyond the ring. The spines are gradually 
developed, and force their way through an enveloping substance which surrounds the stato- 
blast. After a while it often happens that the soft gelatinous envelope is washed away. 
These wonderful objects contain the future young; and the process of development is 
briefly as follows: Within the walls of the parent they attain their full size, and when the 
parent dies at the end of the season, they are liberated and pass from its body. They then 
attach themselves to subaquatie substances, such as vegetables, sticks, stones, etc., and at the 
beginning of the next season the two discs separate, and out comes the young Cristatella, 
ready to take upon itself the tasks for which it was created. It often happens that the two 
discs of the statoblast cling to the young for some time after it has given up its contents, and 
the little creature carries about the separate halves in a manner that reminds the observer of a 
bean newly sprouted from the ground and bearing the two halves of the seed which was 
planted. The Cristatella also produces buds, and in fact, the statoblast is a kind of bud 
of rather peculiar construction. The dise of the statoblast is brown. 
An example of an interesting polyzoon found in ponds and streamlets, and often adhering 
to the rootlets of duck-weed, is the Lophopus crystallinus. Jt deserves peculiar interest as 
being the first species of polyzoa that was detected. The honor of its discovery rests with 
Trembley, who named it appropriately ‘‘Polype a panache,” the plume-like group of ten- 
tacles being sufficiently large to be seen with the naked eye. In this creature, the place of the 
external wall or ectocyst, is taken by a soft gelatinous envelope. 
Mr. Allman remarks that in the interior of the Lophopus are often to be seen a vast num- 
ber of little glittering particles of a pear-like shape, which move about through a series of 
tubes connected with each other like the capillary vessels of the vertebrates. After much 
investigation of the subject, he came to the conclusion that they were merely parasitical. 
Our history of the polyzoa is soon concluded. A fresh-water polyzoon called scientific- 
ally the Aleyonella fungosa, and, popularly, the Fresh-water Sponge, because when dry it has 
a very sponge-like aspect, is found in masses of considerable size, sometimes weighing as much 
as a pound, adherent to various substances which are constantly beneath the waters in which 
it lives. It frequently develops itself round the pendent twigs of the weeping-willow and 
