526 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
(b) Adventitious Homceosis.—(Wheeler: ‘‘redundant or adventi- 
tious homeosis.’’ Przibram: Zusatz-H., Adventive H., Hetero- 
topie.) This form consists in the addition of a formation, which 
normally belongs on another segment, at a point which is already 
supplied with a normal appendage. 
(c) Transpositional Homeosis.—(Przibram: ‘‘ Versatz H.,”’ Trans- 
lation, Heterophorie.) This consists in the transposition of append- 
ages which are absent in their normal positions to points on another 
segment. 
Regeneration is given as the cause of substitutional homeosis; 
this cause seems definitely proved in many of the cases and is pre- 
sumably true for the other cases also. 
As the cause of adventitious and transpositional homeeosis, inher- 
ited variations and embryonic abnormalities both seem to play a 
part. 
Substitutional homeeosis alone has a bearing on the following and 
I shall therefore only consider this form and shall briefly mention a 
few of the rules, which Przibram has proved for this kind of homeo- 
sis: Less specialized appendages always supplant the more special- 
ized if these are removed. As the jointed appendages in the Arthro- 
pods become less specialized the farther back they are found on the 
body, this means that the homeotically changed appendages resem- 
ble the normal appendages on the succeeding joint. This rule does 
not hold for the wings, where the opposite is true; a hindwing will 
thus always be supplanted by a forewing; the opposite has never 
been observed. 
Because regeneration has been proved to be the cause of substi- 
tutional homeeosis in Crustacea and must be supposed to be the cause 
also in insects, this kind of homeosis may be regarded as an extreme 
regenerative Hypotypy. 
In the last part of his paper Przibram calls attention to the char- 
acteristic, striking tendency to homeceosis in certain genera of Crus- 
tacea and insects. Of eight cases within the Lepidoptera, six were 
found in the genus Zygena. All recorded cases in the Coleoptera 
(2+1) were in the genus Prionus, and out of six cases in Crustacea 
five were in the genus Cancer, This is clearly more than accidental. 
It is still more remarkable that this tendency can be traced within 
the different kinds of homeosis; thus only five cases are known 
where a hindwing has been replaced by a forewing; and four of 
these cases were in the genus Zygena, while the fifth was in the 
closely related genus Adela. Transpositional homeeosis is only known 
in the genus Prionus and similar proportions are found in the 
Crustacea. 
Przibram intends to continue his studies on homeosis experimen- 
tally and solicits in his paper material of Prionus, pointing out that as a 
