TUNIC ATA. 3 



multiplication is different^ and the coverings of their bodies, 

 although analogous to the shells of shell-fish, are not shells 

 in their composition and structure. My readers must there- 

 fore be content with a general notice of them, by way of in- 

 troduction to the true molluscs. 



The Tunicata are so named because the body is wrapped 

 up in a kind of tunic or mantle, whicli is thus graphically 

 described by Aristotle, in his work on the History of Ani- 

 mals : — " They are the only kind (of mollusca) whose whole 

 body is enclosed in the shell, and that shell of a substance 

 between true shell and leather : it may be cut like dry lea- 

 ther .'' The " Pather of Natural History " further remarks, 

 " They are attached to rocks by their shells, and have two 

 separate openiogs, which are very small and difficult to no- 

 tice, the ODe to take in, the other to eject the water.^^ 



As these creatures stand among others on the confines of 

 the animal kingdom, it has even been a question whether 

 they belong to it, they seem so very lifeless, and look so 

 much like fungi growing on stones and weeds. Dr. Schmidt 

 indeed found some cellular tissue within them, like that of 

 vegetables ; but this turns out to be only the result of the 

 vegetable substances on which they live, entering into their 

 circulation. 



