1929 ] Present Trends in Systematic Entomology 19 
Taxonomy and phylogenetics are of course so inseparably 
united that it is impossible to deal with any aspect of one 
without considering the other. The structure of the phylo- 
genetic tree is such that it brings into taxonomy a fourth 
dimension which is difficult to deal with nomenclatorially at 
least. This condition is by no means restricted to ento- 
mology, but as we shall see in a moment it promises to 
become more acute with insects than with other groups of 
animals. The development of insect paleontology has until 
quite recently been very slow and restricted to a small series 
of fossil forms, most of them comparatively recent and 
some of the others dating back to what appears to be the 
earlier pages of entomological history. Naturally most of 
these ancient forms are more or less annectant between 
modern orders, and have been grouped taxonomically as a 
very generalized extinct order, Palaeodictyoptera. The re- 
cent discovery of undoubted precursors of particular living 
orders or families and a vast series of genera and species 
before the mesozoic indicates that very soon we shall have 
numerous annectant forms between families and even orders 
that will form a number of taxonomic anomalies. Moreover 
many of the Persian fossil insects are so well preserved that 
their relationships may be very accurately determined. So 
far these fossil forms have generally been placed in separate 
orders, families and genera, but as these rapidly multiply 
and overlap one another they will produce an intolerable 
condition in the nomenclature of higher groups. This is 
more especially true as some groups have persisted over 
long geological periods while others have undergone a much 
more rapid evolution. It is also evident from studies of the 
beautifully preserved insects of early Tertiary age in Baltic 
amber that the same difficulty is arising here among the 
genera of the more recent groups of insects. Some entomo- 
logists still cling to the idea that fossil insects can be dealt 
with as a series apart. Naturally we can deal separately 
with a Permian and an Oligocene fauna but we cannot re- 
gard them taxonomically or nomenclatorially as any more 
independent than the present day faunas of New England 
and Italy. 
An entirely different aspect of systematic entomology 
that has advanced by rapid strides during the last few years 
is our knowledge or the preparatory stages of insects. A 
