440 THE PELON^EA. 



THE simple or solitary tunicates are classed together under the name of Ascidiadse. 

 The common SEA-SQUIRT, figured on the left hand of the illustration, is a good example 

 of the typical genus. 



This animal, in common with all its kin, feeds mostly, if not wholly, upon the minute 

 vegetable organisms, such as the desmids, diatoms, &c. which abound throughout the water, 

 and the manner in which these substances are brought to the digestive organs is equally 

 simple and beautiful " The mouth," writes Mr. Eymer Jones, " is quite destitute of lips 

 or other extensile parts, and situated, not at the exterior of the body, but at the very 

 bottom of a capacious bag inclosed in the interior of the creature. 



It is obvious, then, that whatever materials are used as aliment, must be brought into 

 the body with the water required for respiration ; but even when thus introduced, the 

 process by which they are conveyed to the mouth still requires explanation. 



A truly miraculous apparatus is provided for this purpose. The whole surface of the 

 respiratory chamber is covered over with multitudes of vibratile and closely set cilia, 

 arranged in millions, which by their united action cause currents in the water, all of 

 which flow in continuous streams directly towards the mouth. It is sometimes possible, 

 in very young and transparent specimens, by the aid of a good microscope, to witness the 

 magnificent scene afforded by these cilia when in vigorous action. 



' salientia viscera possis 



Et perlucentes numerate iu pectore fibras.' 



The effect upon the eye is that of delicately toothed oval wheels revolving continually 

 from left to right, but the cilia themselves are very much closer than the apparent teeth, 

 the illusion being caused by a fanning motion transmitted along the ciliary lines, 

 producing the appearance of waves, each wave representing a tooth of the supposed 

 wheel 



Whatever little substance, alive or inanimate, the entering water brings into the 

 branchial sac, if not rejected as unsuitable, lodges somewhere on the respiratory surface, 

 along which each particle travels horizontally, with a steady, slow course, to the front of 

 the cavity, where it reaches a downward stream of similar materials, which hurries 

 onward, receiving accessories from both sides, until at last the whole is brought into the 

 gaping mouth." 



Some of the Ascidia are beautifully coloured with orange, crimson, and white, though 

 others are plain and almost repulsive when dredged from the sea-bed. Several species 

 attain to a considerable size, being five or six inches in length. They do not seem to like 

 deep waters, being mostly found near low-water mark, and seldom at a greater depth than 

 nineteen or twenty fathoms. 



AT the right hand of the illustration is seen another British tunicate. This is the 

 CYNTHIA, one of a rather numerous genus, not uncommon on our coasts. The AGGREGATED 

 CYNTHIA (Cynthia aggregdtd) is to be found on almost any substance that has remained 

 for any length of time below low-water mark, and stones, rocks, wooden piles, or even the 

 larger seaweeds, are frequently covered with these curious creatures, sometimes set in 

 solitary state, and sometimes gathered together in groups by means of the interlacing of 

 the fibres by which they attach themselves. Some species are eaten, Cynthia microcosmus 

 being the most in favour, and regularly brought to market for sale. This animal derives 

 its specific title from the multitude of animal and vegetable parasites that grow upon it, 

 arid so transform it into a little world. 



THE animal which is represented at the upper part of the engraving is the 

 so called from two Greek words, the former signifying mud, and the latter to inhabit. 

 This animal, as its name imports, is in the habit of burying itself in the mud, where it 

 remains fixed and nearly motionless, respiring and obtaining nutrition by means of the 

 two open tubes seen at the smaller end. Only two, or perhaps three, species of this genus 

 are known, and the animal is found in northern Scotland and Norway. 



