320 



Milne Edwards, and Farre, and it is especially to the latter 

 indefatigable and accurate observer that we are indebted for 

 a knowledge of the minute anatomy of these most curious 

 and highly organized polypes. Though in my own investi- 

 gations into the anatomy of the fresh water zoophytes of this 

 order, I have not restricted myself to any particular struc- 

 tures, I yet intend, in the following I'emarks, confining my 

 observations to their muscular system ; reserving for some 

 other occasion the pleasure of directing the attention of the 

 Academy to those points of their anatomy not dwelt upon in 

 the present paper. 



" In the remarks which I am about to offer, it will be 

 seen how closely the ascidian zoophytes of our fresh waters 

 correspond in organization with the marine species ; and 

 though in minute anatomical detail certain differences will 

 be observed, yet these differences are far from invalidating 

 the unity of the type of structure, — a unity which will be 

 found from the following observations to pervade, in a re- 

 markable degree, the entire order. I would wish it to be 

 understood too, that if I should in any respect differ from 

 the statements of Dr. Farre, I offer no opposition whatever 

 to his observed facts, but solely to one or two of the conclu- 

 sions to which they have induced him to arrive. 



" The animal of the present order, to the muscular ana- 

 tomy of which I have chiefly attended, is one which has not 

 as yet been recorded as a native of the British Islands. 

 About two years since I was sent, by Mr. William Thompson 

 of Belfast, to whose researches into the natural history of 

 this country we are so much indebted, a small portion of 

 the dried polypidom of a zoophyte, which he found, in Sep- 

 tember, 1837, cast upon the shore of Lough Erne. From 

 the dried condition of the fragment, — a condition in which 

 the fresh water zoophytes lose all their most interesting 

 characters, — I was unable at the time to arrive at any- 

 thing satisfactory in the investigation of the species ; I 



