Chsetopterns Variopedatus. 517 



sixth or seventh pair of pigmented lines (sixth or seventh setigerous 

 somites). The transverse septa of the setigerous somites extend 

 towards the esophagus as they develop backward from the moutb. 



The stomach is shifted backwards so that its foremost ventral 

 wall is at the level of the fourth pair of pigmented lines (fourth 

 setigerous segment), and its hindmost part extends through one or 

 two segments back of the ciliated rings. In several specimens it 

 was observed to occupy chiefly the widest portion of the body-cavity, 

 that within the second and third ciliary rings. It is a spherical sac 



that completely fills the region to which it is confined. Its walls are 

 thick and have a faint tint of green at this age. 



The intestine is a nearly straight tube in the mid-ventral line. It 

 communicates with the stomach about the level of the third ciliary 

 ring and opens at the anus which is dorsal to the hold-fast. (See 

 text-figure C of Spiochsetopterus. ) 



Luminosity. — The luminosity that is so striking in the adult is 

 present in all the larvae of this stage. It is noticeable in the vicinity 

 of the ciliated rings, and is similarly associated with the mucus 

 which the animals discharge into the sea-water. It is still more 

 noticeable. in the older larvse, in the vicinity of the ciliated rings 

 and the anterior region, when the animals are irritated. 



