482 



LECTCKE XX. 



mass, of which a portion, including three individuals, is shown at A 

 fig. 183, is toughish and semi- 

 transparent. The tubercles with 

 which its exterior is covei'ed, 

 consist each of one end of an 

 individual member of the living 

 group {d d) ; the opposite end 

 of the individual (i i), opens into 

 the cavity of the cylinder. Be- 

 sides the common envelope, each 

 individual has a distinct tunic 

 or mantle attached at the oral or 

 branchial orifice (a, b), at the 

 anal orifice (b), and also to the 

 two rounded bodies (h) at the 

 upper part of the branchite. 

 These {f f) are two in number, 

 oval in form, with their dorsal 

 borders in contact and attached 

 to the mantle, and their ventral 

 borders separated by a large 

 sinus (f) ; their numerous ves- 

 sels anastomose at right angles, 

 and the covering tissue is beset 

 with vibratile cilia, which per- 

 form vortex -like movements 

 with beautiful harmony and 

 rapidity. The oesophagus is curved, and of a bright red colour : the 

 stomach {d) is subglobular, yellowish, and opake : the intestine is 

 short, bent abruptly on itself; the anus {b) directed backwards 

 towards the posterior orifice. The liver {e) is a globular gland, with 

 converging segments : it is attached to the intestinal loop. These 

 viscera ai'e situated posterior to the branchial sac, leaving a free 

 passage to the water which traverses that cavity. The nerve-gang- 

 lion {j) lies upon the anterior end of the branchial sac. The heart 

 is placed at the posterior part of the body, below the visceral mass. 

 In Jig. c, k represents an ovum, and the part marked g in b, was 

 supposed by Savigny to be an oviduct : but the precise condition of the 

 generative organs in the Pyrosoma, is at present not clearly made out. 



The second order of the Tunicata includes the Salpians, which 

 float in the sea, and are chai-acterised by their transparent elastic 

 outer tunic, which is elongated, compressed, and open at both 



Pyrosoma giganteum. 



