REACTIONS OF PROBOSCIS OF PLANARIA . 85 



extend throughout the entire length of the proboscis and open 

 by means of pores along the margin of the mouth. The cell- 

 bodies of these unicellular glands lie within the mesenchyme ven- 

 tral and both posterior and anterior to the base of the proboscis. 

 It is to be noted, therefore, that when a proboscis has freed it- 

 self from the body proper, all of its reactions are carried on 

 without the aid of the cell-bodies of its peculiar unicellular 

 glands. 



NORMAL FUNCTIONING OF THE PROBOSCIS 



Normally, as is well known, the proboscis functions as a pre- 

 hensile organ. When the normal proboscis is ingesting food it 

 is extended and its oral end lies projecting well out beyond 

 the mouth of the proboscis-sheath. The oral end, as it ap- 

 proaches food, opens and closes, operating as a grasping, funnel- 

 shaped structure. In addition to this muscular play of the cir- 

 cular lip of the proboscis, there is a movement of the cilia which 

 line its lumen. This ciliary activity aids in carrying food into 

 the opening and closing mouth. A peristaltic wave arises be- 

 hind the food thus carried into the mouth, and this wave next 

 travels anteriorly, driving the food ahead of it against the closed 

 sphincter of the proboscis. After a mass of food has been col- 

 lected near the sphincter, the latter opens and delivers the food 

 to the enteron. This reaction of the fixed proboscis to food is 

 not to be observed frequently under laboratory conditions. We 

 have seen such reactions only twice, while none of the ninety 

 members of the class in general zoology saw it. Food is not, 

 therefore, readily accepted by the uninjured animals when they 

 are being observed in the small amount of water present as the 

 specimens are studied under the compound microscope. We 

 have, however, been able to feed them with ease when they are 

 retained in watch-glasses containing tap-water, thus making it 

 improbable that the tap-water was highly injurious to the speci- 

 mens, as Walter ('08) found to be the case for the worms and 

 tap-water with which he worked. 



