142 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
always occur with constant regularity. Moreover, in addition to their 
constant form, certain chromosomes 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 monosomes 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 Qualititen 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 evidence 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 
