n8 ELEMENTARY BIOLOGY. [CHAP. 



with a small knob of sealing-wax to prevent it 

 from perforating a passage for itself : the open- 

 ing will be found to lead into a channel which 

 runs along the glandular part of the organ of 

 Bojanus. 



c. Remove carefully the thin transparent roof of the 

 non-glandular part of the organ of Bojanus, on 

 one side, so as to lay bare the portion of the 

 glandular part which lies within the non-glandu- 

 lar: the bristle will be found to leave the passage 

 in the glandular portion by an aperture, which 

 puts it in communication with the non-glandular 

 part, and is situated on the upper side of the 

 glandular part, opposite the posterior end of the 

 pericardium. The glandular part extends back 

 some way beyond this point; but it is imbedded 

 closely in the neighbouring tissues, and is not 

 contained in the loose non-glandular sac, which 

 reaches back no farther than the posterior end 

 of the pericardium. 



d. Examine the floor of the non-glandular part, at 

 its anterior end : in it will be found a small 

 aperture ; gently push a guarded bristle through 

 this : then turn the animal over, and detach the 

 front end of the inner gill on the same side, from 

 the foot. The bristle will be found to have 

 passed out by an aperture (external opening of the 

 organ of Bojanus) which lies just above the attach- 

 ment of the gill to the body. 



6. The gills or branchiae. 



a. Cut out one of the gills and examine it; it will be 

 found to consist of two lamellae united by their 



