1896.] Entomology. 683 
each other by equal structural distances. All that can be reasonably 
demanded of a classification is that its groups of all ranks shall be 
natural ones, and that the higher the groups, the more constant, and 
hence fundamental, shall be the characters by which they are separated. 
Furthermore, it must never be supposed that the variability of a 
character in one group need affect its importance if found to be con- 
stant in another. 
Asa general policy it is evidently desirable that scientific names of 
all grades shall mean as much as possible. The objection to the recog- 
nition of distinct and definable genera and higher groups on account 
of the consequent multiplicity of names is usually to be taken as an 
unscientific willingness to ignore structural differences and natural 
affinities,,in the hope of escaping additional labor. In reality the diffi- 
culty of defining groups containing unrelated members, and of becoming 
acquainted with such through descriptions, much exceeds the temporary 
inconvenience resulting from change of names. 
In attempting to embody in the classification of the Diplopoda a 
recognition of certain structural differences found to be invariable, 
several natural and distinct groups of families have been recognized as 
orders. It is here proposed to render this classification more definite 
and consistent by the division of two of these orders, in the belief that 
the resulting groups, in addition to numerous structural differences, have 
long been divergent in developmental history. The orders thus to be 
divided are the Diplocheta and the Merocheta. From the Diplocheta 
it is proposed to separate the true Iulide and their allies, under the 
name ZYGOCHETA, leaving under the Diplocheta Spirostreptoidea and 
Cambaloidea. The Zygocheta are distinct in many characters of the 
gnathochilarium, in the transformation of the first pair of legs of males 
as clasping organs, the adnate external seminal ducts, the absence of 
legs from the third segment, the presence of legs on the fourth segment, 
and the structure of the copulatory organs of both sexes. The Diplo- 
cheta have the first pair of legs nearly or quite unmodified, the external 
ducts distinct, the third segment with a pair of legs, and the fourth seg- 
ment footless. Notwithstanding these and other important and invaria- 
ble differences, it remains probable that these two orders are more 
related to each other than to any third group of Diplopoda. 
The other case is similar ; the Merocheta will, in the restricted sense, 
contain numerous families allied to the Polydesmide, with twenty closed 
segmental rings; the new order CŒLOCHETA will accommodate the 
