25 
had been overlooked by Fracker, who in 1915 made a careful 
study of the setal pattern of a great many caterpillars. 
The majority of investigators have introduced their own nomen- 
clature for the arrangement of the setae, refusing to accept that ot 
their predecessors, as it repeatedly became evident that each enlarge- 
ment of our knowledge claimed new indications for the details of 
the pattern. Hoping to evade the difficulties, several authors, following 
the example of Dyar, took refuge in ciphers. But this only aggravated 
the confusion, as Dyar himself was obliged after a few years to 
propose a new numbering, which others again tried to emendate. 
So Fracker preferred the notations of the greek alphabet, thinking 
that as their succession was less familiar to our modern minds, it 
would not lead so easily to false conclusions about homologies. 
He designs “one single generalized segment (fig. 1) by plotting, 
one segment over the other, the setae of the prothorax, metathorax, 
and abdomen of the generalized members of the different genera, 
families and suborders of Lepidoptera, as if they all were on the 
same segment.” (p. 17). To this generalized type he ascribes a great 
value, as he believes he has reconstructed by this method the 
ancestral pattern. In those cases where the number of setae is less 
than it should be according to this hypothesis, he explains their 
absence by retrogression (he supposes the absent ones to have 
remained undeveloped). The nearest approach to this generalized 
tvpe he sees in the arrangement of the setae on the prothorax of 
Hepialus, instar [. Yet it must at once be stated that Fracker did 
not observe this species himself, but only judged by a. drawing 
(without accompanying description) of Dyar after Hepialus mustelinus. 
The notation of the setae after FRACKER’s system may be seen in 
Fig. 1. 
In August 1914 Prof. J. F. van BEMMELEN called my attention 
to the question of the arrangement of the setae, and from that date 
onward | have been occupied in investigating the transformation of 
the setal pattern during the larval period of Lepidoptera. The paper 
in full, containing detailed descriptions of the successive instars and 
exact non-schematic figures, will before long be published in: 
Onderzoekingen verricht in het Zoologisch Laboratorium der Riks- 
Universiteit te Groningen. The bibliography will also be given. Here 
may follow only the chief results of my investigations; they were 
obtained before Frackrr’s paper came into my hands, and they are 
often in contradiction with his observations. Moreover they specially 
deal with the youngest instars of the larvae, which FRAcKER dis- 
regarded in most cases. 
