Sonic riioiiomi'na of Rogoner.ilion in Liinnodrilns ;nu\ iclalecl Fornis. 439 



fibers. The wall of (he ton^iie is e.oinpo.sed chiefly of coluninar epi- 

 dermis cells similar to tJiose found elsewhere in the body wall and 

 lining this is a thin layer of nnisele not clearly differentiated into cir- 

 rular and longitudinal fibers (Fig. 24). From Morgan's description 

 one would gather that both are distinguishable in his speciniens, though 

 his drawing does not indieate them clearly. My specinuMis were killed 

 34 to 38 days after the Operation and although Morgan does not State 

 the age of his speciniens they niay have been kept longer, thus allow- 

 ing the differentiation to occur. What might be considered stoma- 

 daeal invaginations of the body wall oecured oecasionally. In the 

 section from which Figure 24 was made a deep lateral infolding of the 

 wall took place near the base of the tongiie but this can hardly be 

 looked npon as a stomadaeuni since these invaginations were found 

 near the tip of the tongue. 



In the cavity itself the most prominent structure is the large 

 mass of nervous tissue which almost fills the basal portion of the tongue 

 (Fig. 24). This tissue appears as a direct continiiation of the ventral 

 nerve cord and bends dorsally so as to almost touch the dorsal wall 

 of the tongue. As Morgan suggests, this probably represents both 

 the cerebral and the suboesophageal ganglia, which have become fused 

 owing to the absence of the intestine. The dorsal part of this mass is 

 somewhat enlarged and its cerebral character is indicated by the fact 

 that small nerves spring from its anterior surface and extend through 

 the cavity toward the tip of the tongue probably representing the nerves 

 which run from the cerebrum into the prostomium of normal indi- 

 viduals. Anterior to the nerve cord there is a blood vessel which 

 has widened out into a sinus and the space surrounding this is filled 

 with both connective tissue and muscle fibers that have wandered 

 from the layer applied to the epidermis. This material forms a loose 

 meshwork ))ut there is no indication of an Organization into septa. 



In this connection it might be well to consider the origin of the 

 mesodermal structures in the regenerated portion at the anterior end 

 of the body. It is a problem, which for some reason has not been so 

 frequently an object of investigation as has the origin of the mesoderm 

 at the posterior end of the body. Some of those who have studied 

 the subject belle ve that, as in tlie case of the posterior end, the meso- 

 derm at tlie anterior end is derived frojn the ectoderm. Such an origin 

 is described by Semper (76) in Nais, Hepke (97) also in Nais and 

 V. Wagner (00) in Lumbriaalu^. However, Iwanow (03) maintains 

 that the secondary mesoderm at the anterior end of Lumhriculiis is 



