EARTHWORM PHARYNX EPITHELIUM. 221 



Therefore the tissues concerned in regenerating these structures 

 could hardly have acquired that power through natural selection. 

 In both cases the source of the regenerating material is an epi- 

 thelium which, originally ectodermal, has come to constitute a 

 specialized part of an internal organ and yet has not lost its primi- 

 tive ectodermal potentialities, or " totipotence." 



BIBLIOGRAPHY. 

 Friedlaender, B. 



'95 Uber die Regeneration herausgeschnittener Theile des Centralnerven- 

 systems von Regenwiirmern. Zeitschr. fiir wissensch. Zool.. Bd. 60, 

 pp. 249-283. 

 Hescheler, K. 



'98 Ueber Regenerationsvorgange bei Lumbriciden. II. Teil. Jena. Zeit- 

 schr., Bd. 31, pp. 521-604. 

 Hiibner, Otto. 



'02 Neue Versuche aus dem Gebiet der Regeneration und ihre Beziehungen 

 zu Anpassungserscheinungen. Zool. Jahrbiicher, Abth. fiir Systema- 

 tik, Bd. 15, pp. 461-494. 

 Vejdovsky, F. 



'84 System und Morphologie der Oligochaeten. Prag. 166 pp. 

 Wolff, G. 



'94 Bemerkungen zum Darwinismus mit einem experimentellen Beitrag zur 

 Physiologic der Entwicklung. Biol. Centralbl., Bd. 14, Nr. 17, pp. 

 609620. 



'95 Entwickelungsphysiologische Studien. I. Die Regeneration der Uro- 

 delenlinse. Arch, fiir Entwickelungsmech. der Organismen, Bd. i, 

 PP. 380-390. 



ABBREVIATIONS. 



bl.v Blood vessel. 



br Cephalic ganglia (" brain "). 



br.f Brain fundament. 



c.c Circum-esophageal commissure. 



c.m Circular muscle layer. 



c.t Connective tissue. 



c.t.s Connective tissue sheath. 



e Epidermis. 



f Fibers. 



l.m Longitudinal muscle layer. 



m Mitosis. 



n.p Non-epithelial (muscular and connective tissue) layer of pharynx 



wall. 



p.e Pharynx epithelium. 



p.n Pharyngeal nerve. 



r.t Regeneration tissue. 



s.g Sub-esophageal ganglion. 



s.n Sub-epithelial nuclei. 



if Region of wound in epidermis. 



