1046 Wlarvels of the Universe 
But best known of all the 
compound forms are those 
popularly termed Starry 
Botryllus. In this division 
of the Ascidian family, the 
individuals are not loosely 
scattered in the investing 
communal tunic, but are 
disposed in little sets with a 
star-like arrangement. Each 
little group or set thus ar- 
ranged is termed a “ system” 
(page 1043), and usually con- 
LARVA OF SEA SQUIRT. sists of from five to ten, but 
A consideration of this diagram will make clear the peculiar structure of these sometimes as many as twelve 
animals. Currents of sea-water enter at a, and exit at b, after passing through the gill : fif 0 a aknalk anh 
chamber c; d is the endostyle; e the notochord; f the spinal nerve. The position of the or teen individuals. ey 
brain is indicated by g, the eye by A, and i, f are the suckers. are always so arranged that 
their inhalent apertures are outward—that is, at the points of the rays—and their exhalent 
cloaca,” in the centre of the star. Dozens, or even 
ce 
apertures are united into what is termed the 
hundreds, of stars are sometimes grouped into one large colony, which, in favourable situations 
—as in sheltered rocky caverns—may form patches eight or ten inches square. All these Starry 
Botryllus are of beautiful appearance. The communal test or tunic—which has a texture very 
much like glossy patent leather—is in some species crimson, in others green, in others purple, 
and in one very common form yellow; whilst the star-like systems present an endless series of 
colorations. A few—but only a very few—of these are shown in their natural size and colours in 
the coloured plate. 
Allied to Botryllus is a form termed Botrylloides. In this the individuals, instead of being 
arranged in star pattern, are set in double rows, and in these there is not much variety in 
coloration, their tints ranging simply from orange to brick-red. A group of these also is shown 
in the plate. 
But whilst all the Ascidians so far mentioned are dwellers in the quiet shelter of rocky grottos 
and the still waters of shady rock pools, there are others whose home is the bounding wave. Many 
species are never attached to rock or weed, but live, either idly floating, or slowly travelling, in the 
open ocean. The best known of these are the Salps. Some of these live singly, such as the Solitary 
Salps (page 1045). Others are in a way analogous to the compound Ascidians, and are affixed 
together in long double chains. In the same group as the Salps is a peculiar barrel-like form termed 
Doliolum, which, in British waters, is usually found of about the size there shown, but in tropical 
seas it is sometimes eight or nine inches in length. 
A wonderful form, which is in the “compound ”’ series, is named Pyrosoma ; many individuals 
are here united into a hollow cylindrical mass, pointed at one end and flat at the other—very like a 
modern cannon-shot. 
The inhalent apertures of all the individuals are outwards as in Starry Botryllus—as may be 
seen in the plate—and the exhalent apertures open inwards into a central cavity which opens out to 
sea at the base, so that the water which is being constantly expelled, propels the Pyrosoma colony 
slowly along. This species is highly phosphorescent, in fact it is probably the most brightly 
luminous of all living things, hence its name Pyrosoma or Fire-body. The individual or “ colony,” 
as we may choose to term it, is shown in the plate of about the size it occurs in these waters, but it 
grows much larger in tropical seas, and there is record of one being netted which was four 
feet in length. 
