102 | BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
converted into a double thread, and at a much later period, after the 
autosomes have become longitudinally split. We may, then, I believe, 
look on the U-shaped monosome of the late growth and maturation 
periods as derived by a longitudinal splitting of the flattened plate of 
the earlier growth stages, the equivalent halves resulting from this 
longitudinal splitting remaining connected with each other at one end 
during the first maturation division, but becoming separated during 
the second maturation division. ‘This interpretation is borne out by 
Stenobothrus, where the division is certainly longitudinal. 
B. Arphia tenebrosa. 
‘The maturation period in Arphia is practically the same as in Dis- 
soterra: >! / 
Figure 64 (Plate 4) shows the metaphase of the first maturation 
division in a cell containing two monosomes. ‘These elements are 
plainly seen, one near each pole of the spindle. However, this con- 
dition is not by any means constant, since in many cases both mono- 
somes are near the same pole. Figures Pa—Pc (p. 100) show three 
successive sections of the same cell during the early anaphase of the 
first division, all the chromosomes being included. ‘These sections 
show conclusively that there are two monosomes, neither of which 
divides during this division, and each is attached to mantle fibers from 
only one pole. In this particular cell the monosomes are passing 
to opposite poles of the spindle. Figure S is a polar view of the meta- 
phase of the second division in a cell which evidently contains both 
monosomes, since there are plainly thirteen chromosomes in the 
equatorial plate. Both monosomes divide longitudinally during this 
division, as does the single one in normal spermatocytes. 
It is obvious that in the case of the individual with two monosomes 
the spermatids might contain eleven, twelve, or thirteen chromosomes. 
C. Hippiscus tuberculatus. 
The maturation period in this species differs little from the same 
period in Dissosteira. . 
D. Chortophaga viridifasciata. — 
The maturation period in Chortophaga agrees in all essential 
respects with that described for Dissosteira. 
