2 BRITISH MOLLUSCA. 



crown of long ciliated tentaciila surronntling their months, 

 and forming so conspicnous a part of the animals, which, 

 aggregated, constitute the plant-like bodies familiar to all 

 frequenters of the sea-shore, and known as Flustr<t. Some 

 of these bodies, such as the Alcyonidium, are extremely 

 difficult to distinguish at a glance from masses or systems 

 of organisms belonging to the true Tunicata. And were 

 activity to be the test of a creature*'s position in the animal 

 series, the little Bryozoa, which form the corallines called 

 Flustra, would stand higher than the Compound Tunicata, 

 for they are infinitely more lively creatures, and apparently 

 even more intelliocnt. Thoush their existence be fixed it 

 is active ; whereas the majority of tunicated mollusks, 

 even of the higher and more independent forms, lead a 

 passive and apathetic life, at least when they have attained 

 their perfect development, for, like many other invertebrated 

 animals, they are much more free and lively in their earlier 

 stages, passing through a tadpole state, but eventually un- 

 dergoing what, in some respects, may be regarded as a 

 retrograde metamorphosis. 



Some very distinguished authorities would separate the 

 whole of the Tunicata from the JNIollusca, and place them 

 as an intermediate class, or sub-class, between that great 

 group and the Zoophyta. Professor Milne-Edwards, 

 whose researches on Ascidians are second in point of merit 

 only to those of Savigny, and, indeed, equal in value, has 

 come to such a conclusion. In his admirable memoir on 

 the " Ascidiens Composees," printed in the eighteenth vo- 

 lume of the "Memoirsof the Institute of France,"" (1842,) he 

 sums up as follows : — " The facts which I have made known 

 in this memoir shew that the Ascidians have less intimate 

 analogies with the Mollusca, jjroperly so called, than is 

 usually believed. They resemble, it is true, these animals 

 in the arrangement of their digestive apparatus, and in 

 some peculiarities of the respiratory system ; but they de- 

 part from the Molluscan type in mode of cii'culation, in the 

 metamorphosis which the fry undergo, and, above all, in the 

 singular power which most of them possess, of multiplying 



