588 A NATURALIST ON THE "CHALLENGER." 



The animal, of which a figure of one-half the natural size is 

 here given, is of a most remarkable form for an Ascidian, having 

 eight conical radially disposed lobes. The walls of the body are 

 perfectly transparent. The animal is provided with a small 

 pedicle for attaching itself to the sea bottom ; but the greater 

 part of its under surface is free and unattached. The usual exha- 



DEEP-SEA ASCIDIAN, OCTACNEMrS BYTHIU3. 



Above. The animal viewed from below of one-half the natural size ; the nucleus is seen in the centre 

 through the transparent base of the animal. P Pedicle of attachment ; B Exhalant orifice ; 

 R Rectum. 



Beneath. Diagrammatic section through the middle line of the animal's body ; A Inhalant orifice ; 

 M Muscle attached to nucleus, other letters as in the figure above. 



lant and inhalant apertures are present, as will be best understood 

 by reference to the diagrammatic section shown in the woodcut. 



There appears to be no gill network present, but the 

 respiratory sac is flattened out so as to be stretched as a 

 horizontal membrane across the cavity of the body between the 

 inhalant and exhalant apertures, as shown in the section. The 

 principal viscera are gathered together into a compact nuclear 

 mass, just as in Salpa, and this nucleus is attached to the under 

 surface of the horizontal membrane. 



The nerve ganglion lies on the nucleus, and there is a glo- 

 bular sense organ in connection with it. Special muscular slips 

 are present on the surface of the nucleus, and there are elaborate 

 muscular arrangements within the conical processes of the body 

 of the animal, and in connection with the horizontal membrane. 

 The animal seems to be entirely without immediate affinities 



