SEA SQUIRTS. 



241 



The flow of water through the branchial chamber is kept up 

 by the regular and unceasing lashing of eye-lash-like cilia y 

 with which the blood-vessels are fringed. This constant inflow 

 at the oral orifice forces the water through to the atrial 

 chamber, from which it is pumped out by the contraction of 

 the mantle. Minute particles of matter that serve as food 

 are also brought in by the current, and find their way into 

 special grooves for their reception and digestion. The other 

 arrangements of the creature are equally simple. The ner- 

 vous ganglion, to which we have made reference, is its only 

 brain, and it has no proper eyes, only some pigment granules 

 near the tentacles appear to be sensitive to light. 



Most of the Ascidians inhabit deeper water than comes 

 within our range, but we shall find specimens at low- water 

 attached to stones and the roots of seaweeds. We may even 

 find specimens of Ascidia mentula in rock-pools, and others we 

 shall discover on smaller stones and shells that have washed 

 in on sandy shores from greater depths. Among such will be 

 the Quadrangular-squirter (Cynthia quadrangtilaris), so-called 

 on account of the squareness of its apertures; and the 

 Currant-squirter (Styela grossularid), a very common form on 

 dead shells, which gets its name partly from its colour and 

 partly from its form when it has closed both apertures and 

 become more rounded. 



But there are many other forms of Tuni- 

 cates that haunt our shores either in deep 

 water or upon the vegetation of the lower z 

 rocks. There are some of more slender, 

 more elongated form that live together in 

 bunches, their bases being connected by a 

 kind of running rootstock, which has the 

 power to produce young individuals by 

 budding from it. This form is known as 

 Clavelina lepadifonnis, and is only about an 

 inch in height, of the form shown in the 



CLAVELINA. 



