238 NATURAL HISTORY OF OUR SHORES 



These are Perophora Listerii. They usually lie, one 

 layer deep, on the clean gritty under side of stones in clear 

 rock pools, when the stones do not lie in close contact 

 with the bottom, but are propped up by others. 



The young student, possessed of a microscope, will do 

 well to collect some of these, and take a supply of sea- 

 water for their observation at home. 



Placed in the hollow of a sunk slip, with a drop of 

 water, and a cover glass lightly laid on (a "Compressorium," 

 supplied by the dealers in microscopes, is the proper, but 

 not actually needed, arrangement), they will show, not only 

 the details of structure given in the diagram, but will show 

 function e.g. that of the curiously acting heart. This organ 

 gives a number of pulsations, usually forty, which propel the 

 blood in one direction. Then there is a few seconds' pause, 

 then an equal number of pulsations sending the current in 

 the reverse direction. This circulation can also be traced 

 in the stolon which connects the individuals. 



Clavellina will show this as well, but it is rather too 

 bulky for the micro slip. 



Where the foregoing are found there will also be many 

 of the compound ascidians. Very common on most shores 

 is MorcheUium argus. The colonies of this one are seen 

 in the form of soft, pear-shaped lumps, about two inches 

 long by three-quarters of an inch in diameter at the wide 

 end, and they hang from the sides, or from underneath 

 the boulders. They are of a brick-red colour. 



One of these clusters pinched between forefinger and 

 thumb into a saucer or watch-glass with sea-water will 

 release the individuals. They are about three quarters 

 of an inch long, slender in form, and of blood-red colour. 

 Each shows, under the microscope, the same details of 

 anatomy as those given in the diagram (Fig. 102). 



In the same, or similar, places may be seen more sessile 

 clusters, of a beautiful rose-pink, with white dots in waved 



