i8 4 



THE NEMERTINI 



The most interesting and characteristic sense organ is the 

 ciliated, neuro- glandular pit at the side of the head (see 5, 11). 



<y 



FIG. XXI. 



Transverse section of DrepanopTiorus albolineatus, Burg, (after Burger), to show the 

 apparent ventral shitting of the lateral nerve cord (e) due to the great development of tlie 

 intestinal caeca (i') and of the diverticula of the rhynchocoel (') ; i, intestine ; p, lateral 

 blood-vessel ; t, dorsal vessel ; w, rhynchocoel ; y, gonad ; j/ genital pore. 



It presents various stages of elaboration, and is only absent in the 

 Mesonemertini, and in such exceptional genera as Malacobdella and 



FIG. XXII. 



Transverse (slightly oblique) 

 section of Langia fonnosa, Hu- 

 brecht (after Burger), a, epi- 

 dermis ; 6, longitudinal muscle 

 of cutis ; c, circular muscles ; 

 d, longitudinal muscles (inner 

 coat) ; e, lateral nerve cord ap- 

 parently shifted dorsalwards ; 

 i, intestine with caecum on left 

 side ; p, lateral blood - vessel, 

 here shifted ventral ly ; w, 

 rhynchocoel ; r, dorso-ventral 

 muscles forming a septum be- 

 tween successive intestinal 



-i! 



Pelagonem^rtes. This organ, which is no doubt phylogenetically 

 derived from the simple pit of some Turbellaria, becomes closely 



FIG. XXIII. 



Cerebral organ of Cerebratuliis 

 in schematic, longitudinal sec- 

 tion (from Perrier, after Burger). 

 AI, Ay, nerve fibres in upper 

 and lower part of dorsal gang- 

 lion ; C, cerebral canal ; E, epi- 

 dermis ; Gl, 01, glands open- 

 ing into the lateral canal (the 

 posterior bunch is proluhly re- 

 presented in Dreparwphonis by 

 the " glandular canal ") ; N, ner- 

 vous tissue of the cerebral 

 organ ; OE, aperture of canal 

 into the posterior end of the 

 horizontal cephalic cleft 



O.E 



e.. 



connected with a special ganglion, or in Heteronemertines penetrates 

 the hinder part of the dorsal ganglion, of which it forms a definite 



