No. 3.] PODARKE OBSCURA VERRILL. 473 



variations, to be explained by the above assumption and not as 

 an ancestral rudiment. 



The most complete examples of rudimentary cells are not 

 explained by either of the above assumptions. These are the 

 small cells described by Conklin and Miss Langenbeck, and 

 tentatively by myself in Podarke, as thrown off from the out- 

 side of the body, or absorbed into the segmentation cavity. 

 These are hardly ancestral rudiments, and yet their fate is 

 difficult to explain on the theory of precocious segregation of 

 formative material. I can offer no satisfactory explanation of 

 the phenomena. 



Oxford, Ohio, March 2, 1899. 



Note. — Since this paper left my hands, March 2d, 1899, 

 several important papers on cell lineage have appeared. See 

 Appendix to Literature. Nothing in these papers has, how- 

 ever, led me to modify any of the views stated in the above. 



Vassar College, January 5, 1901. 



