CLASS VI. TUNICATA: ORDER 2. ASCIDI^. 



531 



COJirOOND ASCIDIANS, MAGNIVIED. 



These animals comprise several extensive groups or families. The Compound Ascidlans, or 

 Botryllidce, are united together by the coalescence of their mantles, so as to form a leathery or 



gelatinous mass, usually attached to stones 

 or sea-weed; in this the separate animals 

 are imbedded round a common canal, 

 many of them being adorned with beau- 

 tiful colors, and these masses are of ai\ 

 ahnost infinite variety of forms. In some 

 cases, the polypidom, or as it is gen- 

 erally called, the Polyzoarkimy is a leaf- 

 like, expanded calcareous mass, attached 

 to a rock, the cells of the separate animals 

 opening by hundreds on one surface only. 

 The Clavcllinidce, or Social Ascidlans, 

 are united by means of a sort of creeping 

 stem, which runs along the surface of sub- 

 marine objects, and gives rise at intervals 

 to short footstalks, at the extremity of 

 which the animals are supported. The 

 separate animals are produced by gemma- 

 tion from the creeping stems, which run 

 in various directions from the base of the original founder of the colony. 



The family of Ascidiidce, or Simple Ascidlans, is composed of animals wliich li\e separately, 

 attached by the base to submarine bodies. They usually form shapeless masses of a cartilaginous 



texture, often of considerable size, Avhich occur in great abund- 

 ance in shallow water. A few species are eaten in some coun- 

 tries. 



The fourth family, the Pyrosomatidce, agree closely with 

 the salpse in the general arrangement of their organs. The 

 colonies of these singular creatures are in the form of a cartila- 

 ginous tube, open at one end. In the walls of this tube, formed 

 by the coalescence of the mantles of the animals composing 

 it, the bodies of the Ascidlans are separately imbedded, the 

 branchial chamber of each passing completely through the Avail 

 from its outer to its inner surface. These animals are found in the seas of warm climates, where 

 they float along in an upright position, but apparently possess no actual locomotive power. 

 Like all the Tunicata, they are luminous in the dai'k, and in fact appear to possess this faculty 



in a greater degree than any other 

 members of the class. Their cylin- 

 drical form, upright position, and con- 

 siderable size, which often exceeds a 

 foot, render them exceedingly beauti- 

 ful objects at night ; and they have 

 been described as resembling little 

 columns of fire. Mr. George Bennett describes a scene which he witnessed at night in the Indian 

 Ocean, in which a ship passed through a shoal of these animals a mile in width, shining like a 

 liquid mass of pale greenish light. The scene was as novel as it was interesting. 



SOCIAL ASCIDIANS, MAGNIFIKD. 



PiUOSOMA. 



Class VII. JBRYOZOA. 



The term Bryozoa is derived from the Greek, hruon, moss, and zoon, an animal, and is descrip- 



I tive of the animals of this class, which always grow together upon a common stock, in the same 



manner as the compound polypi, with which they were formerly arranged. Each animal resides 



