10 BOTRYLLIDiE. 



interesting folio on " The Natural History of Cornwall."" 

 The first naturalist who indicated their compound nature, 

 and held forth a clue to their true affinities, was the famous 

 botanist Gaertner, whose zoological observations on marine 

 animals, communicated to, and published by Pallas, (in 

 1774,) are of the highest degree of merit. Gaertner, how- 

 ever, did not follow up his enquiries in these bodies, though 

 to him we owe the generic groups Botryllus and Distomus. 

 The Italian naturalist, Reniei'i, (in 1793,) had a similar 

 obscure perception of their affinities. 



The memoir of Savigny, published in 1816, however, 

 threw entirely new and unanticipated light on their nature. 

 He shewed that they were essentially Ascidians,diifering from 

 the simple forms only in being united into more or less compli- 

 cated systems. The researches of Milne-Edwards " On the 

 Compound Ascidire of the Channel," read before the Insti- 

 tute of France, 1839, have fully confirmed those of Savigny, 

 and have also greatly extended our knowledge of these 

 creatures. The figures given by both these naturalists are 

 among the most beautiful and minutely accurate that have 

 ever illustrated and adorned natural history essays. 



APLIDIUM, Savigny. 



This genus belongs to the constellated section of the 

 tribe of " Polycliniens " in the arrangement of Milne-Ed- 

 wards. The individual animals of that tribe have a body 

 composed of three distinct parts : 1st, a thorax, with bran- 

 chial apparatus ; 2nd, a superior abdomen, with digestive 

 organs ; and, 3rd, a post-abdomen, with heart and reproduc- 

 tive organs. 



" The common mass of the Aplidia is sessile, gelatinous or car- 

 tilaginous, polymorphous, and composed of very numerous, slightly 

 prominent, annular, sub-elliptic systems, which have no central 

 cavity, but have a distinct circumscription. The animals (three 

 to twenty-five) are placed in a single row, at equal distances from 

 the centre and their common axis. Each has a six-rayed branchial, 

 and a simple indistinct anal orifice." — Savigny. 



