Vol. XLV1I October, 1024 No. 4 







BIOLOGICAL BULLETIN 



CAN THE EARTHWLRM PHARYNX 1 EPITHELIUM 

 PRODUCE CENTRAL NERVOUS TISSUE? 



MIRIAM F. NUZUM AND HERBERT W. RAND, 

 ZOOLOGICAL LABORATORY, RADCLIFFE COLLEGE. 



It has long been known that, when several segments of the head 

 end of an earthworm are removed, within a comparatively short 

 time a new head will be regenerated. The first of the new tissues 

 to be differentiated is the nervous tissue. Hescheler in 1898 de- 

 scribed in detail the regeneration of the nervous and other organs 

 in several species of earthworm. He believed the mass of " Re- 

 generationsgewebe " from which the nerve cells differentiated to 

 be largely of epidermal origin. This would seem to be the natural 

 source of nerve material, since in the embryo the nervous system 

 is formed by a thickening and infolding of the ectoderm. 



The operation in which several head segments are removed in- 

 volves loss to all of the tissues of that region. Consequently re- 

 generation is an extensive process in which all of the injured tis- 

 sues must be more or less concerned. But if the cephalic ganglia, 



1 The region of the alimentary canal referred to here and throughout the 

 paper is so precisely at the junction of the buccal cavity and the muscular 

 pharyngeal region as to occasion doubt whether its epithelium should be desig- 

 nated as buccal or pharyngeal. It is very slightly anterior to the heavy dorsal 

 muscle of the pharynx. Transverse sections through the brain fundament of 

 worms regenerating after an operation of the kind described in this paper in- 

 variably include the " Schlundcommissuren," and the " Schlundganglien " or 

 " Schlundgeflecht " (Vejdovsky, 1884; and other authors) consisting of heavy 

 ganglionated nerves passing from the commissures to the wall of the alimentary 

 tube. " Schlund/' at least for the Lumbricidae, must have the sense of pharyn- 

 geal. The term "circum-esophageal commissures," commonly used in English 

 texts, is inappropriate for Lumbricidae because the commissures are remote 

 from the esophagus. Vejdovsky (1884, p. Si) says: "Die Schlundcommis- 

 suren umgreifen den Pharynx. ..." In view of these facts we designate the 

 region in question as pharyngeal rather than buccal. 



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