520 CLARENCE E. McCLUNG 



cytologically and taxonomically. In the course of this study of 

 the more extensive series of preparations a number of facts have 

 been determined which were obscure in the early stages of the 

 investigation. Although it is not yet possible to present a 

 complete study of the two genera, owing to failure to secure cyto- 

 logical material from all the species, there are some facts known 

 which should be presented in ordqr to add what has definitely 

 been determined and to correct errors in the earher description. 



Since the appearance of my former paper ('05) upon multiple 

 chromosomes, a number of observations upon similar structures 

 have been reported by different investigators. Some of these, 

 such as the ones of Voinov ('14), are not clear in their nature, but 

 recent papers by Robertson ('16) and his student, Woolsey, ('16) 

 have made distinct contributions to our knowledge of chromo- 

 some relations which will certainly prove valuable. These are 

 strongly confirmatory of the view expressed in my former papers 

 ('05, '08) regarding the persistent organization of chromosomes 

 even in the face of apparent numerical reductions. Very strik- 

 ing is the discovery of a structure, the octad, which I was not 

 then able to find, but whose existence I anticipated so strongly 

 that I gave it a name in advance of its actual observation. The 

 occurrence of such a multiple chromosome I am now abundantly 

 able to confirm, as well as the steps in its formation reported by 

 Woolsey. The underlying principles of chromosome organiza- 

 tion, permitting the anticipation of yet unobserved conditions, 

 stands in as striking contrast to the conception of chance asso- 

 ciation of undifferentiated masses as does the periodic law of 

 chemists to the vagaries of the alchemists. 



In this reexamination, advantage has been taken of the un- 

 usual opportunities for a study of the taxonomic characters of 

 the two genera, especially Mermiria, offered by the splendid 

 collections at the Philadelphia Academy of Natural Science 

 under the charge of Messrs. Rehn and Hebard. Much good is 

 sure to come from their active interest in all that concerns the 

 group upon which they are specializing and from their cordial 

 and generous cooperation with other students. By their very 

 careful studies of large numbers of excellently preserved speci- 



