558 ON THE STRUCTURE AND HABITS 



along their course, and at the end a membranous dilatation, 

 from which springs a thread encircled by a beaded line, which 

 at first is convoluted and doubled on the base, and then ac- 

 companies the thread to the end. The peduncles of these 

 latter tendrils, about an inch in length, are fixed higher on the 

 side than the former; but seem exceedingly liable to injury, 

 since it is rare that all of them are perfect. The membranous 

 threads appear to be the branchiae, but the anterior branched 

 tendrils seem rather to be absorbent organs, like the roots of 

 a tree, affording the only source of nutriment, which I ima- 

 gine to be assimilated in the reddish side of the internal sac; 

 and which, besides its redness, is of a rather thicker substance 

 than the surrounding structure. 



In its healthy state the colours of this animal are beautiful ; 

 the crest being striped alternately with light blue and crimson 

 or pink, and the sides similarly tinted, with reflections. The 

 tendrils are of a darker blue, and sometimes a dull purple. — 

 Examined within there is a thin membranous structure, which 

 is necessarily pierced when the cavity is opened. On its an- 

 terior portion it is firmly attached to what I have denominated 

 the oral space ; it is also, but very slightly, attached posteri-, 

 orly ; and along the upper margin there is a varying number 

 of branched appendages, each of which occupies a portion of 

 the chambers of the crest. In some specimens, where the 

 crest is low, they are fewer, less branched, and more obtuse ; 

 in others, long, slender and much divaricated. In the living 

 state this membranous structure is so closely applied to the 

 external muscular parietes, as not to be discerned through it, 

 the cavity appearing empty. They are also so little adher- 

 ent, except at the end, as to separate spontaneously ; but still 

 between them both is a slight villous coat, adhering to the 

 external or containing portion, and which is the chief, if not 

 the only seat of the colour. It is probable that the chief in- 

 terchange of vital action is through this structure, which, al- 

 though so slight and unadherent, is as closely connected as 

 in some other animals or structures in which no more certain 

 mode of communication has been traced. Many morbid 

 growths in the human body have even less connection with 

 the common vitality. This internal sac contains nothing but 

 air, which appears to be secreted into it by the crest, that 

 being its chief, if not the only office. No trace of food can 

 be found, nor any separate organization, except a reddish 

 thickening, already alluded to, at one portion of the surface. 

 It is this which appears externally ; and it seems just to owe 

 its appearauce to vascularity, though no separate vessel can 

 be distinguished ; it is probably the seat of the vital actions, 



