142 bulletin: museum of comparative zoology. 



always occur with constant regularity. Moreover, in addition to their 

 constant form, certain chrorhosomes have a definite mode of attach- 

 ment to the mantle fibers, which persists throughout all the generations. 



In the case of the allosomes, as has been urged by a number of 

 writers, we have very strong evidence in favor of the individuality of 

 the chromosome. Certainly there can be no doubt that in many cases 

 at least these elements retain their individuality from one generation 

 to another. This is especially true of Steiroxys, where the monosome 

 can be followed continuously from the primary spermatogonia to the 

 spermatid. Furthermore in the case of Arphia we have in one indi- 

 vidual two monosomcs persisting throughout the spermatogenic cycle, 

 and this abnormality is constant for all the testicular elements. Similar 

 phenomena have been described by Stevens (:06*) and Zweiger (:06). 



But this morphological differentiation of individual chromosomes 

 must mean a corresponding physiological differentiation, as was first 

 clearly brought out by Boveri and Sutton. Boveri's (:02) remarkable 

 experiments, which are too well known to require discussion here, have 

 led him (:04) to conclude: "Somit bleibt keine andere Annahme 

 iibrig, als dass die Variationen, die wir in der Entwicklung dispermer 

 Keime angetroffen haben, auf verschiedener Kombination von Chro- 

 mosomen beruht, und dies heisst nichts anderes, als dass die einzelnen 

 Chromosomen verschiedene Qualitaten besitzen miissen." This 

 is entirely in accord with the morphological differences in form and 

 volume, for, as Montgomery (:06) has pointed out, chromosomes of 

 different size cannot have the same physiological value but must have 

 activities differing at least in amount. Moreover, the constant differ- 

 ence in form which has been shown to occur can be explained only 

 on the basis of a physiological difference of which the form is the 

 expression. Then, too, we have the CA'idence of the allosomes, whose 

 functions as indicated by their very different form and behavior must 

 be quite unlike that of the autosomes. Further, there seems to be 

 little question that, as first argued by Sutton (:03), we are justified in 

 concluding that the paternal and maternal components of each auto- 

 some pair are practically alike physiologically as well as morpholog- 

 ically. Such a physiological similarity would explain the intimate 

 relations which are found to exist at all times between the compo- 

 nents of each pair as well as their conjugation during synapsis. This 

 would also indicate, as first suggested by Sutton (:02) and later elabo- 

 rated by Boveri (:04), that possibly the conjugation of the chromo- 

 somes during synapsis is not so much to allow for an intermingling of 

 the substance of the conjugants as to afford a simple means of insuring 



