56 Invertebrate Zoology, 



most beautiful ciliary motion will be observed. Note the 

 supporting bars and the openings through the gill-lamella 

 for the passage of water. This passes from the infra- 

 branchial chamber into the water-tubes between the lamel- 

 lae, and thence into the supra-branchial chamber. The 

 supra-branchial chambers of the right and of the left side 

 open into a common cloaca, below and behind the pos- 

 terior adductor. From the cloaca the water reaches the 

 exterior through the upper siphonal or excurrent canal. 



Make drawings of all the parts of the respiratory appa- 

 ratus. The arrangement of the supra-branchial chambers 

 may be well shown by imaginary cross-sections. 



The Circulatory System. The location of the heart 

 within the delicate pericardium has already been noted. The 

 organ will be found to consist of a median and strong-walled 

 ventricle into which opens, from each side, through an au- 

 riculo-ventricular opening, a thin, triangular-shaped auricle. 

 The lower side of the auricle, corresponding to the base of the 

 triangle, lies above the supra-branchial chamber and receives 

 the purified blood from the gills. The rectum, or posterior 

 portion of the intestine, passes through the ventricle. In- 

 jected specimens will clearly show the course of the arteries 

 as they pass anteriorly and posteriorly from the heart. The 

 bulbus arteriosus will be noted on the posterior aorta as a 

 large contractile sac. 



The Excretory System. The kidney, or organ of 

 Bojanus, has already been noted. Examine under the 

 organ and near its anterior end. Two small openings will be 

 found. The more posterior is the opening of the ureter, and 

 leads from the kidney. It lies inside 1 the second, the repro- 

 ductive opening. If a hair is carefully passed into the open- 



1 Nearer the median plane. 



