PELONAIA, A NEW GENUS OF TUNIC ATED MOLLUSKS. 439 



chial artery in a corresponding course below, so that the 

 threads of attachment of the plaits on the external surface of 

 the sac are fixed into the tubes, in a series on each side. 



Anatomy of P. corrugata* 



The structure of this species differs very little from that of 

 the P. glabra. The animal being elongated, the organs are 

 placed more longitudinally. The respiratory sac is longer, 

 the stomach is longer, and is not placed so much across the 

 body. The oesophagus runs down to the bottom of the sac 

 before it terminates. The rectum is very long, and of con- 

 siderable width, but just before it terminates in the anus, it 

 becomes very much contracted. The mantle exhibits no 

 ridge or shelf below the anal orifice, but its longitudinal fibres 

 are very .strong, and form a thick bundle at their origin round 

 the respiratory opening. The test, instead of being thin and 

 diaphanous like parchment, as in P. glabra, is thick, carti- 

 laginous in appearance, coloured brown, and transversely 

 wrinkled externally. 



From the details of structure which we have now given, it 

 is evident that the Pclonaice are Ascidice. Their anatomy is 

 important, as it explains the nature of the parts and organs in 

 the Tunicata. They differ from the other A scidiai more parti- 

 cularly in being bilateral. The generative organs are sym- 

 metrical, and open one on each side of the anus, which is 

 directed towards the ventral surface of the animal, in a line 

 with the mouth and nervous ganglion. The latter is thus 

 proved to be an abdominal or sub-oesophageal ganglion, corre- 

 sponding to, or forming one of the chains of ganglia on the 

 abdominal surface of, the articulata. In the Bame manner 

 the branchial artery or heart is proved to be the pulsating 



-/ 



Additional details, with Bome modifications in the description, hare 

 recently been given by Dr, W. C. M'Intosh, in tiio Annals of Natural History, 

 June i $03 . Eds, 



