Planar ians. 



59 



FIG. 35. 



CLASS I. Turbellaria. The simplest worms 

 with which we are acquainted are found on the sea- 

 shore, under or adhe- 

 rent to stones, or else 

 in fresh-water pools, 

 as small, ciliated, flat- 

 tened soft bodies, 

 which glide with a 

 slug-like motion over 

 wet surfaces, or swim 

 by the vibrations of 

 their cilia. These 

 Turbellarians (so call- 

 ed from the commo- 

 tion produced by their 

 cilia in the water 

 around them) have a 

 mouth placed gene- 

 rally beneath, not at 

 the anterior extremity* 

 and the part of the 

 digestive canal im- 

 mediately within the 

 mouth is protrusible 

 as a kind of proboscis. 



This COn tains, in SOme Polycelis Iczvigatus, a common Turbellarian. 



7 a. mouth ; b, buccal cavity ; <r, opening of 



Ol the larger forms, a oesophagus ; d, stomach ; e, caecal branches 



. . of stomach; f, nerve ganglia ; g; spermatic 



Spine Or dart, Which gland .; A, vesicular seminars ; /, spiculum ; 

 1 k, oviducts ; /, spermatheca ; m< mouth of 



is used as a weapon oviduct. 



of offence, and being supplied with poison from a little 

 poison-gland at its base, acts as a formidable weapon 

 against the minute creatures upon which these animals 



