PHYLUM CHORDATA 



363 



and ends in the anus. Like the earthworm, this animal utilizes the 

 mud in which it lives for food, absorbing the organic matter from it 

 as nutriment. Balanoglossus has numerous paired gill slits, located 

 in the lateral walls of the anterior (supposedly pharyngeal) position 

 of the digestive tube. In some of the other representatives the gills 

 are much reduced in numbers or are lacking. Where gills are pres- 

 ent, water is passed through them for respiratory purposes, oxygen 

 being absorbed and carbon dioxide being discharged from the 

 blood here. There is no differentiation of a distinct pharynx. 



Fig. 209. — External features of DoUchoglossits kowalevskii. 



Denoyer-Geppert Company. ) 



(Courtesy of 



Proboscis coelom 

 Proboscis 



Pericardium 

 Glomerulus / Collar 



Heart / 



Nerve cord 



Dorsal vessel 



Trunk 



Notochord Mouth 



Ventral vessel 



Gill slits 



Alimentary canal 



Fig. 210. — Diagram of a sagittal section through anterior portion of Dolicho- 

 glossus. (From Hegner, College Zoology, published by The Macmillan Company, 

 after MacBride.) 



The circulatory system is rather rudimentary. It includes a 

 sinuslike heart which is held in a pericardial sac located in the basal 

 part of the proboscis. A dorsal vessel extends posteriorly from the 

 heart to the posterior end of the trunk. At the collar it is joined by 

 lateral connectives which encircle the body to connect with a ventral 

 vessel extending posteriorly below the intestine. Sinuslike branches 

 of these main vessels supply various parts of the body. 



The nervous system is composed of a dorsal cord which is tubular 

 in the region of the collar and extends the length of the trunk, a 

 more or less concentrated center of nerve cells in the collar, and a 



