232 ARTHUR E. SHIPLEY. 



brain, I am disposed to think that the main function of the 

 tentacles is to create a current, and thus bring food to the 

 mouth ; and the chief use of the vascular system is to extend the 

 tentacles. 



I am inclined to look for the chief respiratory organ in the 

 intestine ; this has very thin and extensive walls, and exposes a 

 large surface to the coelomic fluid, which in its turn bathes all 

 the organs of the body except the brain. A considerable 

 volume of water passes through the alimentary canal, enough 

 to supply the oxygen required, and this current is maintained 

 by the ciliated cells of the groove in the ascending intestine. 



The Moephological LABORATOEy, 



Cambeidge; August, 1891. 



EXPLANATION OF PLATE XV, 



Illustrating Mr. Arthur E. Shipley's paper on '^Onchne- 

 soma Steenstrupii." 



Pig. 1. — An enlarged view of 0. Steenstrupii, with the introvert 

 partially retracted. 



Fig. 2. — The same, life size. 



Fig. 3. — A view of the arrangement of the internal organs, shown by opening 

 the body-wall along the right side and reflecting the sides. Copied from 

 Koren and Danielssen. 



Fig. 4. — Section through a portion of the glandular wall of the nephridium, 

 showing the glandular cells and their concretions. 



Fig. 5. — Section through the ascending intestine to show the ciliated 

 groove. 



Fig. 6. — Section through the skin, parallel with the long axis of the body, 

 showing cutis, epidermal glands and their secretions, circular and longitudinal 

 muscle layers, and lining peritoneal cells. 



Fig. 7. — Longitudinal section through the posterior end of the body, 

 showing origin of single retractor, and the group of peritoneal cells which 

 form the testis. 



