294 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



(i.) The sinus venosus. In the plane of this section this 

 is a small, delicate walled chamber (y), on the median line, 

 and its upper wall forms part of the floor of the pericar- 

 dium. 



(a. ) Pass a bristle backward into the part of this cham- 

 ber which has been cut off posterior to this section. The 

 chamber will thus be found to end blindly behind. 



(6.) Pass another bristle forward into the anterior part 

 of the chamber, which will be found to widen, and at its 

 anterior end an opening will be found through which its 

 cavity communicates with that of the pericardium. 



(ii.) On each side of the sinus venosus are the sections 

 of the wide, flat, non-glandular, chambers of Bojanus (z). 

 Their upper walls form part of the floor of the pericar- 

 dium, and are thin and transparent. 



(iii.) Below these, and meeting each other upon the 

 median line below the venous sinus, are the thick- walled 

 glandular chambers (t) of the organ of Bojanus. 



(a.) Select the slice which has been cut off between 

 this section and the one next behind it, and pass a bristle 

 into this last chamber, and another into the non-glandular 

 chamber of the same side ; they will be found to pass out 

 together, thus showing that the glandular and non-glandular 

 chambers are in communication posteriorly. 



(6.) Select the portion of the body anterior to this sec- 

 tion, and introduce bristles into the same chambers and 

 pass them as far forward as possible. No communication 

 between the two will be found, but it will be seen that the 

 non-glandular chamber does not lie above the glandular 

 throughout its whole length, but that their anterior ends are 

 side by side, and that each forms part of the floor of the 

 pericardium. 



(c.) If care is used, the bristle which has been passed 



