Studies on Regulation. 511 



tapering, the pharynx is smaller and the intestinal branches in the 

 new tissue are shorter and less numerous in pieces without ganglia; 

 the differences between pieces with and those without ganglia are 

 much greater during later stages of regeneration than during the 

 earlier; and they are also greatest when regeneration occurs from 

 a level not far posterior to the ganglia, and decrease as the level 

 of the cut surface approaches the posterior end. 



8. The effect upon regeneration of the removal of parts of the 

 ganglia depends upon the amount of tissue removed. Removal 

 of about half the ganglionic tissue is followed by complete 

 regeneration, but if more than half be removed regeneration is 

 slight. The result is the same whether the part removed be 

 anterior, posterior, or lateral. The relations between the ganglia 

 and regeneration are thus similar to those between the ganglia 

 and motor activity (see 3). 



9. The experiments indicate that the cephalic ganglia do not 

 exercise any "formative" influence upon posterior regeneration. 

 The differences observed between pieces containing the ganglia 

 and those without them are readily explained if the conditions 

 connected with functional activity of the parts, and in these cases 

 especially motor activity, are regarded as formative factors. Thus 

 the relation between the nervous system and posterior regenera- 

 tion is indirect, not direct. The presence of some part of the 

 central nervous system is, however, necessary for the continued 

 existence of a piece and so indirectly for regeneration. 



Hull Zoological Laboratory, 



Hull Zoological Laboratory, 



University of Chicago, Chicago, 111. 



February, 1904. 



BIBLIOGRAPHY. 



Bardeen, C. R., '01.— On the Physiology of the Planaria maculata with especial 

 Reference to the Phenomena of Regeneration. Amer. Journ. of 

 Physiol., Vol. V, 1901. 

 '02. — Embryonic and Regenerative Development in Planarians. Biol. 



BulL.Vol. Ill, No. 6. 1902. 

 '03. — Factors in Heteromorphosis in Planarians. Archiv. f. Entwicke- 

 lungsmech., Bd. XVI, H. 1, 1903. 

 Child, C. M., '02. — Studies on Regulation. I. Fission and Regulation in Stenostoma, 

 Archiv. f. Entwickelungsmech., Bd. XV, H. 2 and 3, 1902. 



