340 N. M. Stevrns ajid A. M. Boring. 



and "totipotence" of material (Morgan, '04) modified in many 

 cases by the folding under and uniting ot the anterior cut 

 surfaces. 



It is the intention of the authors to supplement this work with 

 further experiments during the coming summer. 



PART II. HISTOLOGY. 



BY 



A. M. BORING. 

 With 2 Plates and i Figure in the Text. 



After working on the external features of the regeneration of 

 Polychcerus caudatus in California during the past summer, Miss 

 Stevens brought back to Bryn Mawr some preserved material — • 

 the whole flatworms and pieces that had regenerated for varying 

 lengths of time. The simplicity of structure and the lack of any 

 great differentiation of tissue, made it a matter of interest to work 

 out the histological side of the regeneration of this form, in order 

 to see whether it differs in any essential points from the method 

 of regeneration in more highly differentiated forms, such as 

 Planaria simplicissima, described by Stevens ('oi), and Planaria 

 maculata, worked out by Curtis ('02) and Thacher ('02). 



Technique. 



The material had been fixed in a mixture of corrosive subhmate 

 and acetic acid, the regenerating pieces at the end of one, two, five, 

 seven, ten, fourteen, and twenty-eight days. After being hardened 

 in the alcohols, and embedded in parafiine, the whole worms were 

 sectioned in transverse and sagittal planes, and the regenerated 

 pieces in transverse, sagittal, and frontal planes. The sections 

 were stained in Delafield's haematoxylin, followed by orange G. 

 This combination gives a good differentiation of the various 

 tissues. The reproductive cells stain purple, the mucus blue, the 

 nuclei of the parenchyma cells brown, the parenchyma itself pale 

 yellow, the muscle cells deeper yellow, and the cilia usually form 

 a slightly stained border at the margin of the sections, in parts of 

 which the separate cilia can be distinguished. 



