94 EDMUND B. WILSON 
the other types (C-G),* or the more complicated ones shown in 
fig. 5. I represents the possible mode of separation of the 
X-element from a YY-pair, as suggested by Stevens; and this 
may be realized in Ascaris megalocephala (H). J and K are. 
schemes of the relations seen in Hesperotettix, Anabrus and 
Mermiria (cf. fig. 6). These may be direct derivatives of a 
primitive XY-pair, as the diagram suggests, or may be a result 
o C. Thyanta Be 
B. letochromosome &; xf D. Fitchia 
si 
A. Primitive E. Conorhinus 
1 ee CNS ee 
G. Syromastes 
Al 
T A. Mermiria 
FL Ascaris wi oe, elyria 
Hesperotellix 
Fig. 7 Diagram illustrating the possible relation of the various types of idio- 
chromosomes to a primitive XY-pair. Explanation in text. 
of secondary coupling of X with other elements. In either case 
X may itself have such a composition as is indicated in F (Prote- 
nor). 
(c) Sea-limited heredity. (1) The foregoing considerations have 
an important bearing on the problem of sex-limited heredity, 
for they give us a very definite view of how such heredity may be 
effected. It is not my intention to consider this subject in ez- 
8 These figures are not intended to indicate the precise mode of segregation of 
the X- and Y-chromatins of the X-element, but only illustrate possible modes. 
