358 THE BOLT EN I A. 



TUNICATA. 



The strange-looking creatures, as the Plonsea, the Sea-Squirt, the Clavellina, etc., have 

 long perplexed systematic naturalists, and even now, although they have been the subject of 

 careful examination by accomplished zoologists, many parts of their economy are enigmatical 

 in the extreme. The order to which they belong is called by the name of Tunicata, because 

 the animals possess no shell, but are covered with an elastic tunic. Some of them are trans- 

 parent and really beautiful, while others are apparently little more than shapeless masses of 

 gelatinous substance, studded with minute stones, fragments of shells, and coarse sand, over- 

 grown with sea-weeds, and perforated by certain bivalve mollusks. 



The simple or solitary tunicates are classed together under the name of Ascidiada?. The 

 common Sea-squirt 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, etc., which abound throughout the water, 

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

 aud beautiful. "The mouth," writes Mr. Rymer 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 How in con- 

 tinuous 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 maguihcent scene 

 afforded by these cilia when in vigorous action. 



' salient i a viscera pnssis 



Et perlucentes numerare in 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 appear- 

 ance of waves, each wave representing a tooth of the supposed wheel. 1 ' 



Another tunicate is the Cynthia, one of a rather numerous genus, not uncommon on 

 European coasts. The Aggregated Cynthia {Cynthia aggregata) 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 sea-weeds, 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 favor, 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, and so transform it into a little world. 



Our next example is the Pelon.ea, so called from two Greek words, the former signi- 

 fying 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 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 Scot- 

 land and Norway. 



The curious Boltenia, so called after Dr. Eolten, a naturalist, of Hamburg, is found 

 in rather dee]) 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 



