140 
Thos. H. Montgomery, jr. 
tliere caiinot be continiüty of chromosomes. But such constancy is by 
110 meaiis necessary for our theory, for it is based inost strongly upon the 
phenomeiia of the regulär recurrence from one mitosis to another of par- 
ticular chromosomes, or pairs of them, constantly recognizable by pecu- 
liarities of form, size and behavior, and upon the phenomena of the 
recognizable persistence even during the rest stage of the modified chro- 
mosomes (allosonies). The literature on insect spermatogenesis is replete 
^yith such cases, and demonstrates that in some instaiices chromosomal 
continuity may be associated with inconstancy of number of chromo- 
somes, as niy present study of Euschistus and Wilsox’s study of Meta- 
podius show. Della Valle objects to Wilsox’s results the difficulty of 
recognizing particular chromosomes -with absolute certainty ; but he falls 
to notice that in many such instances there is no such difficulty. 
ln the second place many of the cases that Della Valle cites 
from the literature in support of his thesis really do not furnish any e^^- 
dence for it, and we may mention some of these. Thus in the cases of 
Trichopepla, Metapodiiis and Anasa the chromosomal variabUity is due, 
according to all describers except Foot and Strobell, to the presence 
or absence of a particular, definite allosome. Some other cases entered 
in his list do not really embody individual vaviability in the number of 
the univalent elements, but variability in the number of the bivalent chro- 
mosomes of the fh'st maturation spindle, as Euschistus, Harmostes, Corizus, 
Chariesterus, Lygaeus and Tingis. Certain others of his list are not ad- 
missible cases, e. g. : the parthenogenetic (therefore abnormal) cleavage 
ceUs of Strongylocentrotus; the spermatogonia of Syrhula, for which f 
stated that my material probalily comprised more than one species; and 
the case of the erytlirocytes of Salamandra, where the observer (Török) 
paid no particular attention to the number of the chromosomes and 
Della Valle counted them upon the published figures of this observer! 
Other cases have no reliability on account of the small number of chromo- 
somal counts, such as Leptynia, Pyrrhocoris and Homo. In some other 
instances tabulated by hini it is practically certain that the numerical 
Variation obtained was due to chromosomes being hidden or partiaUy 
obscured, or to the difficidty of deciding whether a constricted chromo- 
some should be counted as 1 or 2 (a mistake I have made in some of my 
earlier papers). Again it is curious that for Ascaris megalocephala he 
cites only vom Rath and Wasiliewski, but does not mention Brauer 
or Hertwig. Further, Della Valle unjustifiably tabulates different 
counts as given in successive papers of a particular author, whereas he 
sliould have tabulated the results of only the last (revised) paper; and 
