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 watere where it is exposed to the full blaze of the meridian sun. The 

 ordinary length of the Oistatella 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 is a 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 discs, 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 subaquatic 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 disc 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 LopJiopiis crystallinus. It 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 Alcyonella 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 



