532 



MOLLUSCA. 



ill a si-parali' (h^II, wltliin wliidi it .an usually n-trart itself entirely; the cells are sometimes soft 

 ami llexil.io, soiiictiincs l...ni\ , and s.-uutiiiies calcareous. Tliey frequently stand ujx.n short foot- 

 stalks, risiiit; from a tul)ular stock, wliicii creeps over the surface of stones and aquatic plants. 

 In other eases the cells are .sessile, forminiX a crust upon submarine objects, while in others the 

 .•oh)iiy is attached only by its base, with the opposite extremity lloatinjr freely in the water. In 

 these the stock is more or less branched and often leaf-like. They possess ciliated tentaeula 

 placed at the anterior extremity of the body. Tlie colonies are increased by gemmiparous repro- 

 duction. Tin; ••lass is .jividcd into two orders, the Lophopoda and Infundibulata* 



ORDER 1. LOPHOPODA. 



Tn tliis order, composed of inliabitants of fresh water, the tentacles, which are more numerous 



than in the preceding, are placed upon a pair of 

 long arms, which spring from the sides of the 

 upper extremity of the animal, and usually de- 

 scribe somewhat the form of a horse-shoe, as is 

 seen in the Plumatella. Their cells are usually 

 of a leathery texture, nearly transparent, and 

 usually spring from a root-stock of similar con- 

 sistence, which creeps along upon the surface 

 of stones or aquatic plants, in which situations 

 these animals are not uncommon. In some 

 species, however, as in the Cristatella, the 

 polypidom floats freely in the water, and is of a 

 gelatinous consistency; in these the animals 

 composing each colony are usually three or four 



PLUMATELLA. ^^ ^""^^6^' 



ORDER 2. INFUNDIBULATA. 



This order derives its name from infundibulum, a funnel. It includes a great number of genera, 



presenting an infinite variety of structure. The common Flus- 

 trce, or Sea-Mats, are flat and foliaceous in their form, pre- 

 senting a considerable resemblance in appearance to pale-brown 

 sea-weeds, with which they are in f;xct generally confounded 

 by sea-side visitors. But when carefully examined, these 

 leaf-like bodies will be found to consist of a multitude of 

 small horny cells, opening at the surface ; and from each of 

 these, when the polypidom is placed alive in a vessel of 

 sea-water, the little creatures may be seen protruding their 

 tentacles. Many nearly allied species grow upon the fronds 

 of sea-weeds, over which they spread like a thin coating of 

 gauze, composed of similar cells, opening of course only on one 

 side. Others are found incrusting stones and other submarine 

 bodies with a cellular calcareous mass. In many species the 

 cells are an-anged so as to form a more or less threadlike, 

 branching polypidom ; while others are furnished with a creeping root, from which the cells lise 

 by stems of greater or less length. All the Infundibulata are marine animals. 



FLUSTRA AVICULARIA ; NATURAL SIZE. 



* The Ttinicnta and Bnjozoa—ih^ Pyrozoa of some authors — were formerly arranged with the Polypi, thoii!;li now 

 placed with the Mollusca ; they are, however, so peculiar in certain respects as to constitute with some naturalists 

 a separate division under the name of Molluscoid-ea. 



