TIIH PROCTUCFIA. 



L*8 



the same fundamental type abound among tbc polychaetous 

 Annelida, the Ecldnodermata, and the Mottusca. 



FIG. 34. A, young Tetrctfitemma.aa^ central Ganglia of the nervon? system; 66. cil- 

 iated fossae ; c, aperture through which the proboscis is protruded; d, anterior 

 portion of proboscis ; , posterior muscular part, fixed to the parietes at/; g, in- 

 testine; A, anal aperture; i, water vessels; *. rhythmically contracting vessels. 

 (After Schulze.) B, anterior extrcMiiitv of the everted proboscis of Jttrastemma, 

 exhibiting the principal aud the reserve etilets. (After Schulze.) 



The lowest Proctucha, such as Microstomum, have no 

 frontal proboscis (whence they are termed Arhynehia), and 

 they differ very little from the lowest RJutbil- \o in the 



fact that there is an anus, and that the sexes are distinct. 

 But all the other Proctucha (Rhynchocoeld, or Nemerteans) 

 are provided with a frontal proboscis, which sometimes oc- 

 cupies the greater part of the length of the body (Fig. 

 It has special retractor muscles, and its internal surface is 

 either merely papillose, or may possess a peculiar armature, 



