48 
Psyche 
[March 
as the Plecoptera only tracheae could be seen in the developing wings, 
and that the pattern of venation of the adult wing agreed closely 
with the pattern of tracheation in the wing pad, they concluded that 
tracheae determined the positions of the veins (Comstock, 1918, 
p. 12). They also concluded that the ontogenetic history of the 
tracheal pattern recapitulated the phylogenetic history of the vena- 
tion in the group of insects concerned. Applying these principles to 
the Odonata and Ephemeroptera, for example, they reached the un- 
expected conclusion that a branch of the radius vein had crossed 
over a branch of the media in the course of the evolution of these 
groups; the trachea appeared to cross over in the wing pad and this, 
in their view, meant that the vein had done likewise in previous 
geologic time. Objections to the tracheation theory of vein deter- 
mination and especially to the recapitulative conclusions were raised 
by several students of fossil insects and insect evolution (e.g., Till- 
yard, Martynov, Carpenter, Fraser) in the period from 1923-1935. 
In 1935, Needham reiterated his stand on the ontogenetic-phylogenetic 
relationship of tracheae and veins; and in 1951, he published a more 
detailed discussion in defense of this thesis, especially as it related 
to the Odonata, although a substantial part of his paper was an at- 
tempt to ridicule in a personal manner all individuals who had dis- 
agreed with him. 3 * 5 
As Needham himself indicated (1935, p. 129) there had not been 
undertaken up to that time a thoroughgoing investigation of the de- 
velopment of nymphal wings of any species, at least with respect to 
the development of tracheae and veins. Shortly after, however, such 
an investigation was made by Holdsworth (1940, 1941), this con- 
sisting of a histological study of the development of wing pads, 
tracheae and veins, starting with the earliest beginnings of the wing 
buds. The plecopteran, Pteronarcys , was chosen because Comstock 
and Needham considered the stone-flies as demonstrating most clearly 
the tracheal determination of veins. Holdsworth’s results were 
strikingly clear: the tracheae did not enter the main area of the 
wing pads until the blood spaces or lacunae between the blocks of 
epidermal cells had already established the positions of the veins. 
The tracheae, as they grew longer, simply entered the lacunae which 
had already been blocked out, following the lines of least resistance. 
Variation in the tracheal branching was obvious and usually several 
3 One can only regret that this final paper on this subject by Needham 
was so vindictive. It contributed nothing to science and detracted from 
Needham’s image as a scientist. It also earned a black mark for the Amer- 
ican Entomological Society for publishing it. 
