MARINE BIOLOGICAL STATION AT PORT ERIN. 123 



and mode of life of Ascidia, but these would require many 

 figures and a microscopic examination of the animal for 

 their exposition. Another simple Ascidian which we 

 frequently have in the Aquarium is Styelopsis grossularia 

 (2), " the red-currant squirter of the sugar-loaf rock," as 

 it has been called, because of the myriads which cover 

 with a red papillated surface many square yards of the 

 cliif in the beautiful caves near Spanish Head. 



Compound Ascidians are colonies each member of 

 which is very much like a Simple Ascidian in structure, 

 but they are all united together by one covering or tunic. 

 A common and very brightly coloured kind of Compound 

 Ascidian is Botryllus, shown at 5 in fig. XXV., and 

 commonly found under stones about low-water mark. The 

 colony is marked with bright stars and wheels, each ray of 

 which is a separate member of the colony, with complete 

 organisation of its own. There are many other kinds of 

 Compound Ascidians (such as that shown at 4) ; they rival 

 the sponges in their curious shapes and brilliant 

 colours. No. 3 is Clavelina, where beautifully transparent 

 individuals are united by a creeping root. It is sometimes 

 found in the deeper rock-pools at Port Erin. 



The egg of an Ascidian develops into a minute 

 tadpole-shaped larva which has a back-bone running 

 along its tail and a nervous system with a brain, contain- 

 ing an eye and an ear. In fact, the structure of this 

 Ascidian larva is very like that of any young vertebrate 

 animal, and if it remained in this condition for life it 

 would be proper to classify it along with the lowest fish- 

 like vertebrates. But it does not so remain. After a brief 

 free-swimming existence it becomes attached to a rock or 

 sea-weed, and settles down for the rest of its life. Then 

 degeneration sets in. The backbone, the brain, the eye 

 and the ear — all the evidence of its high organisation and 



