296 LIFE BY THE SEASHORE. 



In addition to the simple sea-squirts there are a great 

 number of colonial forms, in which the small individuals 

 are embedded in a common test, a number being usually 

 grouped round a common atrial opening. Very abundant 

 are the species of Botryllus, in which the colony spreads as 

 a great sheet of jelly over stones, the surface being studded 

 by little stars with a central hole. Each star is a cluster of 

 individuals grouped about the common atrial opening, while 

 the test of the simple Ascidian is represented by the sheet 

 of jelly in which the individuals are placed, and which 

 connects the clusters together. The colonies, for the most 

 part, avoid the light, and are to be found beneath stones, 

 and under overhanging rocks, but they are usually bright in 

 colour purple, greenish, yellow, and red tints being common. 



Along with Botryllus the species of Botrylloides also 

 occur, in which, instead of being in stars, the individuals 

 are arranged in long, double rows, which branch and 

 anastomose in a complicated fashion. The colonies form 

 their incrustations on the rocks just as Botryllus does, 

 and occur in similar localities. Where representatives of 

 these two genera occur freely, there will probably also be 

 representatives of other genera of compound Tunicates, 

 which in some cases, instead of being flat, form little 

 stalked masses of jelly. They can always be recognised as 

 Tunicates by the occurrence of the individuals, or zooids, 

 embedded in a common jelly, and in many cases it is easy 

 to pick out a zooid on a needle, and with a lens demonstrate 

 the existence of all the parts which we discovered in the 

 simple sea-squirt. But though the Tunicates compound or 

 simple are an interesting group, we must not linger over 

 them, for, generally speaking, they are too difficult as 

 regards their minute structure for most amateurs, and the 

 distinctions between even the genera rest, in most cases, on 

 minute points. 



Finally, we come to the Fishes, of which we can name 

 only a few of those which haunt the rocks at low water. 

 Everyone who has watched fish in their natural surroundings 

 must have been struck with their singular beauty and grace; 

 cold, slimy, and shapeless as they seem when dead, in life 

 they are full of energy and vitality, as beautifully adapted 



