THE PYROSOMA 44, J 



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 

 illustration. The CLAVELLINA may be seen lying upon the leaf of the laminaria, the 

 different 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 colour, 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 connexion 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 increase the general mass. 



THE Botryllidae, 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 shell of these animals, are fused into a 

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

 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 branchial 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, i.e. Fire-body, is an example of the next family. This is one of the compound 

 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 .gorgeous 

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



