1 84 



THE NEMERTINI 



The most interesting and characteristic sense organ is the 

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



FIG. XXI. 



Transverse section of Drepanophorus albolineatiis, Biirg. (after Burger), to show the 

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

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

 blood-vessel ; t, dorsal vessel ; w, rhynchocoel; y, gonad ; y" 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 Lanqiaformosa, Hu- 

 brecht (after Burger), a, epi- 

 dermis ; b, longitudinal muscle 

 of cutis ; c, circular muscles ; 

 d, longitudinal muscles (inner 

 coat) ; e, lateral nerve cord ap- 

 parently shifted dorsal wards ; 

 i, intestine with caecum on left 

 side ; p, lateral blood - vessel, 

 here shifted ventrally ; w, 

 rhynchocoel ; x, dorso-ventral 

 muscles forming a septum be- 

 tween successive intestinal 

 caeca. 



Pelagonemertes. This organ, which is no doubt phylogenetically 

 derived from the simple pit of some Turbellaria, becomes closely 



FIG. XXIII. 



Cerebral organ of Cerebratulus 

 in schematic, longitudinal sec- 

 tion (from Perrier, after Burger). 

 AI, ^2> nerve fibres in upper 

 and lower part of dorsal gang- 

 lion ; C, cerebral canal ; E, epi- 

 dermis ; Gl, Gl, glands open- 

 ing into the lateral canal (the 

 posterior bunch is probably re- 

 presented in Drepanophorus 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 



connected with a special ganglion, or in Heteronemertines penetrates 

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



