208 PROCEEDINGS OF THE ACADEMY OF [Feb.^, 



ON THE GERM CELLS AND THE EMBRYOLOGY OF PLANARIA SIMPLISSIMA.. 



BY N. M. STEVEXS. 



This planarian, which is found in small streams about Bryn Mawr. 

 was identified provisionalh' in 1900 by Woodworth as Planaria luguhris, 

 and has since figured under that name in several of Prof. T. H. Mor- 

 gan's papers on regeneration; also in my "Notes on Regeneration in 

 Planaria lugubris" (Stevens, '01). 



On looking up the European species (P. luguhris) as described and 

 figured by Schmidt ('59, PI. Ill, figs. 5 and 6), and by Kennel ('79, 

 PI. VII, fig. 8), I felt sure that Woodworth must have been mistaken as 

 to the species; but I was unable to find any correct description or 

 figures, either of the external characters of the animal or of its repro- 

 ductive organs, and I was inclined to call it a new species. In Sep- 

 tember, 1903, after this paper was written, I came across an article 

 by Curtis ('00) on the reproductive organs of Planaria simplissima 

 n. sp. The reproductive organs of this species were so strikingly like 

 those of the form on which I had been working that, although there was 

 considerable difference in form, size and color, I was convinced that 

 the two worms must be closely related, if not local varieties of the same 

 species. 



In answer to m^^ inquiries about Planaria simpUssima , Prof. Curtis 

 has recently written me that after studying specimens sent to him b}' 

 Prof. Morgan from Brjoi Mawr, and sectioning others of the same spe- 

 cies found near Baltimore in 1900 and 1901, he concluded that the 

 Williamstown form, P. simplissima (fig. B), and the Bryn Mawr form 

 P. {luguhris), (fig. A) belonged to the same species. Prof. Curtis 

 desires me to state that his description of the external characters of 

 P. simplissima was made from fixed material, living specimens not 

 being accessible when he discovered that he was dealing with a new 

 species. Later observations on living specimens from Williamstown 

 made it apparent that his description was at fault, especially with re- 

 gard to the lateral cephalic appendages which are more marked than 

 was evident in fixed material. A careful sketch, made at this time 

 from the living animal and sent to me with his letter, is a good repre- 

 sentation of a young specimen of the Bryn Mawr form (figs. A and B) 



