INDIVIDUALITY OF CHROMOSOMES. 13 



have been directed toward reducing them to a single type or 

 form, or to show that all accomplish the same purpose and that 

 the variations are only chance differences or certain stages in the 

 development of the tetrad or stages in the first spermatocyte 

 division. 



It is impossible to discuss within the limits of this paper all the 

 works that have described and discussed a variety of chromo- 

 some forms in the spermatocytes and ovocytes. For such dis- 

 cussions I would refer the reader to Wilson's "Cell," p. 264 ff., 

 and Korschelt and Heider's " Entwickelungsgeschichte," p. 

 572 ff. 



Wilson's interpretation of these different shapes is evident from 

 this quotation : " But even in cases where the chromatin does 

 not condense into actual tetrads these bodies are represented by 

 chromosomes in the form of rings, crosses and the like, which 

 are closely similar and doubtless equivalent to those from which 

 actual tetrads arise, and present us with the same problems. 

 With a few apparent acceptions described hereafter, the tetrads, 

 or their equivalents, always arise by a double division of a single 

 primary chromatin rod or mass." Wilson then discusses the 

 various maturation divisions and chromosome shapes under : 



() " Tetrad formation with one longitudinal and one trans- 

 verse division," naming Henking's, Vom Rath's, Haecker's, et al. 

 results. 



(&} "Tetrad formation with two longitudinal divisions," Van 

 Beneden and Boveri on Ascaris. 



(c] "Tetrad formation by conjugation," Wilcox and Calkins 

 especially. 



In these cases the rings, etc., occur in the prophases. 



" Reduction without tetrad formation" occurs where there is 

 no resting stage and here "the equivalents of tetrads," the rings, 

 crosses, etc., appear. Again, the divisions are longitudinal and 

 transverse, found mostly in Invertebrates, or double longitudinal, 

 found mostly in Vertebrates and in many plants. 



Korschelt and Heider classify the various mitoses under " cnnii- 

 totic" or double longitudinal, and " pseudomitotic" or one longi- 

 tudinal and one transverse a reduction division. After dis- 

 cussing very many papers giving the various forms of chromo- 



