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4 MISC. PUBLICATION 344, U. 8S. DEPT. OF AGRICULTURE 
the interspace between the anterior and posterior spiracles, one oppo- 
site the posterior spiracles, and one on the segment behind these. 
It is assumed that the anterior cluster is located on the head, and 
it seems evident that the posterior cluster is on the first abdominal 
segment, but to avoid possible misinterpretation of the basic morphol- 
ogy of these insects these clusters are designated in the subsequent 
descriptive notes as prespiracular, anterior “spiracular, intermediate, 
posterior spiracular, and first abdominal. Apparently this first ab- 
dominal segment is the transition point between these structures and 
those often designated as plates. The duct tubercles on this segment 
tend toward oreater elongation than in the anterior clusters, and 
generally one or two recognizable plates are evident at the posterior 
corner of the segment. The condition outlined above appears to be 
maintained for all the species here discussed except blanchardi and 
zizyphus. In blanchardi these duct tubercles appear to be entirely 
lacking. In zzyphus the anterior groups are lacking and the remain- 
ing tubercles are much reduced in size and very short conical, while 
the duet opening is proportionately much larger than in the remain- 
ing species. 
DORSAL TUBULAR DUCTS 
Two groups of dorsal tubular ducts are here considered. One is 
the cluster or band of submarginal ducts which appears on each side 
of the body, on the abdominal segments, and which varies greatly in 
number of included ducts, depending on the species, but also, un- 
fortunately, varies conspicuously within the species. As here ac- 
cepted, this eroup of ducts embraces all these large, short tubular 
ones except those of the single row along the edge “of the abdomen, 
which are clearly marginal. The numbers in a group may range from 
as few as 7 to more than 100. Usually the posterior duets are lar gest, 
and the size decreases gradually anteriorly, Presumably these ducts 
have a definite seomental arrangement, but this is usually obscured by 
their apparently unrestricted distribution over the surface of the 
abdominal segments involved. 
The second group of dorsal tubular ducts comprises those 
occupying the medial portions of the abdominal segments. In this 
discussion these ducts are designated as intermediate and median 
macroducts or microducts, according to their location and size. The 
difference between macroduects and microducts is probably purely arbi- 
trary and in some species shows some tendency to break down through 
individual variation, but usually there is no difficulty in deciding 
whether the ducts are large enough to be classed as macroducts, such 
appearing as reduced copies of the lar ge marginal and submar gimal 
tubular ducts, or should be classed as microduets, which have the 
tube proper many times longer than the opening. The intermediate 
ducts as here defined may occur from a point between the anterior 
paragenital pore clusters, when these are normally oriented, to the 
anterior apex of the abdomen, but they most frequently appear in a 
cluster above the anterior paragenitals and in a row or cluster on 
the segment preceding this, eenerally at the margin of the sclero- 
tized area normally present on the dorsum of the pygidium. Their 
arrangement is obviously segmental. The median ducts cecur less 
frequently and when pr esent are to be found on or close to the median 
