BREATHING MECHANISM OF THE LAMPREYS. 109 



frequently happens that a violent contraction of the branchial 

 region follows, accompanied by a discharge of the carmine from 

 the mouth. At the moment of this discharge the external 

 branchiopores are seen to be closed as noted under 20. 



26. If a stream of thick carmine mixture be directed gently 

 into the oral funnel of a free Lampetra wildcri or Ichthyomyzon 

 concolor so as to fill the funnel, it frequently happens that there 

 is a violent contraction of the branchial sac, accompanied by a 

 stream of water which issues from the mouth and expels the car- 

 mine solution. At the same time the external branchiopores 

 are seen to be closed as noted in 20. 



27. It is concluded from 25 and 26 that a current of water 

 from the gill sacs forward through the water tube, pharynx and 

 mouth cavities is the agent by means of which these lampreys 

 habitually cleanse pharyngeal and mouth cavities and is the 

 only means by which bodies too large to pass into the alimen- 

 tary canal or through the branchiopores, may be removed. 



28. The current of water directed forward through the mouth, 

 by means of which these lampreys are able to detach themselves 

 and to cleanse the mouth cavity and pharyngeal cavity affords 

 the first adequate explanation of the function of the valves of the 

 external branchiopore, of the water tube and of the velar valve. 



29. In the free Iclitliyoinyzon conco/or, by the use of carmine 

 and water, a gentle current may sometimes be seen entering the 

 mouth during the inspiration and passing out through the gills. 



30. The teeth of the oral funnel of Petromyzon niarinns are so 

 arranged in concentric loops that when moved in radial lines by 

 the action of the annularis muscle they lacerate every part of the 

 surface with which the funnel is in contact. 



3 i . The tongue of the attached Lampetra ivildcri or IcJitJiy- 

 oinyzou concolor may be thrust forward so as to bring its teeth in 

 contact with the surface of its host and thus when the animal is 

 feeding the lingual teeth aid those of the oral funnel in lacer- 

 ating the tissue of the host. 



32. When the tongue is thrust forward in these attached lam- 

 preys so that it no longer serves to maintain the vacuum in the 

 mouth cavity by closing the cavity posteriorly, the semiannularis 

 muscle is believed to contract and thus to maintain the closure 



