THE PYROSOMA. 441 



THE curious BOLTENIA, so called after Dr. Bolten, a naturalist, of Hamburg, is 

 found in rather deep waters, being sometimes drawn up by fishermen's lines from a 

 depth of seventy fathoms. The animals of this genus are attached to long footstalks, 

 at the end of which the creature sways like a fritillary on its slender stalk. The two 

 orifices by which water is admitted into and ejected from the system are seen, and 

 their remarkable four-cleft openings are well displayed. When very young, the Boltenia 

 is often found affixed to the stem of its parent. 



WE now arrive at the Social Ascidians, two examples of which are given in the illus- 

 tration. The CLAVELLINA may be seen lying upon the leaf of the laminaria, the dif- 

 ferent individuals being united by long filaments. The blood circulates through these 

 channels of communication, passing to and fro through separate tubes. It is a small 

 creature, and extremely transparent, the latter characteristic making it a valuable 

 species to the physiologist, who is enabled to watch its structure, and the methods 

 in which the different organs perform their duties, without needing to dissect it. 

 The Clavellina may be found on the English shores at low water, adherent to rocks, 

 stones, or seaweed, to which it attaches itself by means of the tiny root-like projections 

 which are developed from the outer tunic, something like the little rootlets by which 

 ivy clings to a wall. 



OUR second example is the SYNTETHYS, another British species, which is seen affixed 

 to the stone on the right hand of the illustration, spreading flower-like from a small 

 base. When full grown, a group of these creatures forms a largish mass, nearly six 

 inches in diameter, and as many in height, each member of the group being about two 

 inches long. They are rather transparent and of a greenish color, and, when touched, 

 they will contract themselves violently, and vanish into the common mass on which 

 they are seated. These animals are propagated both by eggs and buds, the buds being 

 produced on offshoots of the creeping tube. Sometimes the young one severs its con- 

 nection with the parent, and fixes upon some fresh locality, there to form the basis 

 of a new colony, but it frequently remains on the same spot, and only serves to in- 

 crease the general mass. 



THE Botryjlidas, or Compound Ascidians, are represented in our list by the common 

 BOTRYLLUS, the star-shaped animal which is shown under and a little to the right of the 

 syntethys. The " tests," or equivalents of the shells of these animals, are fused into a 

 common mass in which these individuals are imbedded. In the present genus the ani- 

 mals are arranged in a star-like form, each group consisting of a number of individuals, 

 not less than six, and not more than twenty, in number. Many of these groups, or 

 systems as they are technically called, are found upon the common test. The bran- 

 chial orifices are simple, and the other orifice is common to all the members of the 

 group, and forms, as it were, the centre of the radiating star. Six British species are 

 known, which may be found on stones and seaweed at low-water mark. 



A VERY beautiful and curious mollusc, called from its luminous appearance the 

 PYROSOMA, /. e. Fire-body, is an example of the next family. This is one of the com- 

 pound tunicates, and looks like a gelatinous cylinder, open at one end, and closed at 

 the other, and having its body covered with numerous zoids grouped in whorls. A 

 large Italian-iron tube, studded with daisies, will give a good idea of its general shape. 



The ejecting orifices of the aggregated animals all open into the hollow interior of 

 the cylinder, and the consequence of this structure is, that by the constant flow of the 

 rejected water, the whole mass is driven slowly and regularly through the waves. When 

 seen at night they look just as if they were made of glowing white-hot iron, and they are 

 at times so numerous as to choke up the nets of the fishermen, and diffuse so strong a 

 light around them that even the fishes are rendered visible when they happen to swim 

 within the sphere of its radiance. There is generally a greenish hue about the light. 



Of the appearance presented by these animals when existing in great numbers, 

 Mr. F. D. Bennett gives the following vivid and valuable account : " When assembled 

 in the sea, and, as is usually the case, near the surface, these creatures present a gor- 

 geous spectacle ; their vivid phosphoric light being sufficient to illuminate, not only the 



