530 Mr. W. S. Mac le ay's Anatomical Observations 



Tethya of Aristotle, or les Ascidiens of Savigny, I cannot do bet- 

 ter than cite the description given by the ancient philosopher, 

 and mentioned above. 



In his Historia Animalium, under the head of Testaceous Ani- 

 mals (ra oa-T^etKoiB^i^a.), he observes that " there are some, such as 

 those called T^dva, which are so entirely surrounded by their test 

 or envelope* as to have no part of their flesh exposed." So far 

 this accurate and philosophically drawn character may apply to 

 the whole of the Tunicata : but Aristotle afterwards proceeds to 

 describe the Tethya in the following more definite terms. " But 

 of all these animals (viz. ra, oa-T^axoh^f^a), those which are called 

 Tethya"^ have the most remarkable nature : for with them alone 

 is the body entirely concealed in the test. This test or envelope J 

 (to offT^axov) is between the texture of leather and shell, and may 

 consequently be cut like a piece of tough hide. The animal 

 adheres to the rocks by its test, and has two passages or ori- 

 fices (To^ous), distant from each other, and so small as not to be 

 easily visible. By means of these it imbibes and discharges the 

 water. 



" On opening one of these animals, the inside presents, in the 

 first place, a membrane composed as it were of nervures§ (u^iW 



* 'Em Vol oXa TTipts^eTcu too ocrrgaxo) x«i ouflsv t^j ffagxoj i^st elf to e^co yu/ivov, oTov 

 Tot xa\ou|u.eva T^Sua. 



•f- As Aristotle afterwards mentions the colours of such species of Tethya as he was 

 acquainted with, it seems probable that his species were the Ascidia microcosmus Cuv. 

 and Ascidia papillosa Linn. 



;}; In the original, "to S'oVTpaxo'v lo-Tiftsrafu legiiarai xa) oa-Tpaxou," This passage is 

 curious, as showing Aristotle's disposition to generalize ; a disposition so rare among 

 modern comparative anatomists, that we need not be surprised at observing some of 

 them to be perfectly ignorant of Natural History. 



^ This is a good description of the beautifully reticulated membrane which forms 

 the branchiae of the Tethya, and will be easily understood on referring to the dissection 

 of Dendrodoa glandaria, as given PI. XX. fig. 5. Aristotle appears, however, by some 

 mistake to have considered the branchial pouch as surrounding the intestine. 



