358 CONTRIBUTIONS TO THE NATURAL HISTORY 



lateral lobes, whence the tube continues in a very complicated course through the lobe 

 and towards the mouth, and also towards the large lobe. First, the tube follows the 

 inner margin of the small lobes, then turns round their obtuse points and retraces a 

 parallel course in an oblique direction ; but the base branches in such a way as to unite 

 simultaneously with a tube extending along the margin of the mouth, and with another 

 extending into the large lobe, or it may rather be said, that an anastomosis is established 

 at the base of the small lobes, on their external margin, with the chymiferous system of 

 the large lobes, as well as with that of the margin of the mouth. Fig. 3 of Plate VII., 

 in which the inner surface of the anterior lobe is turned outwards for the whole extent 

 of its margin, shows this connection most distinctly. The anastomosis with the large 

 lobe is established through a tube which arises from the lower sinuosities of the inner 

 convolution of the long ambulacral tube. The communication with the oral tube is more 

 direct, and may be considered as a branch from the tube of the short ambulacra ; indeed, 

 both may be considered so, the anastomosis with the large lobe, as well as that with the 

 mouth. But, in the first case, the communication with the tube of the long ambulacra 

 is more indirect than it would be if it were placed in the course of its terminal sin- 

 uosities, where it forms frequent anastomoses ; while the connection with the oral sys- 

 tem is direct, through a tube which only bends at right angles upon itself. What is the 

 meaning of these numerous anastomoses upon the inner surface of the large lobes I 

 cannot tell. Are they of the character of the gills of Brachiopods and Ascidians, or 

 are they something of a nature more peculiar to these animals ? This remains to be 

 investigated. 



But so much is certain for the present, that the large lobes and the small lobes are 

 not fully identical. The large lobes are a mass of the same gelatinous substance which 

 constitutes the principal portion of the body ; while the small lobes seem simply mem- 

 branous, and are really hollow sacs, a kind of diverticula arising from a folding of the 

 surface of the body at the lower extremity of the short ambulacra. These lobes are, 

 indeed, a mere fold, and the direct prolongation of the short ambulacra in every respect, 

 though they seem as completely different from the ambulacra as they are from the large 

 lobes. However, upon close investigation of their structure (Pate VIII. Fig. 8), it is 

 found that their margin is encircled by vibrating cilia, and that the ambulacral tube 

 follows the base of those cilia all round the margin of the lobe, until the cilia of the 

 lobe disappear in their turn, and the tube alone is continued, branching, as mentioned 

 above, into the large lobe, as well as towards the margin of the mouth. 



Upon these considerations, we may, therefore, view the small lobes as a simple 

 modification of the lateral ambulacra, bent inwards in proportion as the great transverse 



