182 FLORENCE BUCHANAN. 



be seeiij and directly outside the circular muscle layer comes the 

 ccelomic epithelium. Neither of these last two layers takes any 

 share in the folds. 



In one specimen which I had, which was evidently a young 

 form with only about twenty segments, the alimentary canal 

 was wide, and constricted intersegmentally in all the anterior 

 segments of the body as far back as the 10th. Between the 10th 

 and 11th segments was a deep permanent constriction, the canal 

 continuing very narrow throughout the rest of the length of the 

 body. This would seem to imply that the pharyngeal and 

 oesophageal region of the alimentary canal developed late.^ In 

 this specimen there was green pigment all down the sides of 

 the alimentary canal, not, as far as I could see, enclosed in any 

 way. There were also no thoracic nephridia. 



Like so many other Chsetopods, this one has almost con- 

 stantly present parasitic monocystes in its intestine, and these 

 are often very numerous. They are broad at one extremity 

 (apparently the anterior), and usually pointed at the other 

 (fig. 13). The cortical substance forms a clear zone, wider at 

 the anterior extremity. The medullary substance is coarsely 

 granular, and in it, reaching to the posterior extremity, is usually 

 a long narrow vacuole {vac), which may sometimes be found 

 bursting. Sometimes they have no vacuole, and such I at 

 first mistook for eggs, until finding that they were in the 

 alimentary canal and not in the coelom. They may be seen 

 moving backwards and forwards with the intestine, apparently 

 incapable, while in the body at least, of any independent motion 

 of their own. The nucleus (w.) is spherical and well marked^ 

 containing a nucleolus. 



Vascular System.^ — There is a contractile dorsal vessel 



' But it may be that the oesophagus i s developed, but resembles the part 

 of the intestine following it in being intersegmentally constricted, since this 

 appears to be the case in the larva of what is probably a Spio or Nerine 

 described by Leuckart in the ' Arch. f. Naturg.,' 21st Jahresg., 1S55, p. G3, &c., 

 and pi. ii, fig. 1. Here, however, I did not observe anything marking off the 

 two regions of the alimentary canal from one another, as Leuckart describes in 

 his larva. 



- The whole arrangement of the vascular system is not easy to determine, 



