690 General Notes. [ November, 
the insects, and the Coleoptera in the neighborhood of the Hemiptera 
and Orthoptera, where they unquestionably belong. 
Mayer adopts the suggestions of Biitschli and Semper that the air-tubes 
of insects originated from the segmental organs of worms, and, discard- 
ing Gegenbaur’s view that the air-tubes were at first internal, closed air- 
sacs, he believes that the stigmata or breathing holes were the first to 
be formed. It may be objected that as insects are already provided 
with renal vessels, it is not necessary to suppose that segmental organs 
(also in part excretory) survived in them, and the inquiry arises whether 
the air-tubes of insects may not have arisen from the water-vascular 
system of the lower worms, which communicates with two or more ex- 
ternal openings. In framing hypotheses like these, one guess may be 
as good as another. 
The author, in a foot-note, combats with considerable unction our 
suggestion, made in 1867, that the head of insects consisted of seven 
segments. It may be observed that at that time we were influenced by 
the prevailing views of Agassiz, Dana, and others, who regarded the 
ocelli and eyes as homologues of the limbs. This view was corrected 
in the Memoirs of the Peabody Academy of Science, ii. 21, 1871 (a 
work from which our author quotes), and also in several other places, 
including the Guide to the Study of Insects, third edition, 1872; and the 
view that the normal number of cephalic segments is four was at the 
same time and in the same places insisted upon. 
Dr. Mayer also quotes us as believing that the parts of the ovipositor 
are not homologous with the legs, a view we suggested in 1866, but 
after fresh embryological studies retracted in the above-mentioned Mem- 
oir in 1871 (which the author seems to have read), and also in other 
places, notably the essay on the Ancestry of Insects, quoted by Mayer, 
where the view that the ovipositor of the Hymenoptera, Hemiptera 
(Cicada), and Orthoptera, as well as the spring of the Thysanura and the 
spinnerets of spiders, are homologues of the legs is emphasiz 
As regards the position of the primitive band of insects, Mayer ignores 
the remarks of Dr. Dohrn on its significance in classification, and con- 
siders that the circumstance whether the primitive band is external sf 
floats within the yolk, is of much importance, laying down the law that 
“insects with an external primitive streak are in gene : 
those with an inner.” We have previously * objected to Dohrn’s classifi- 
cation of insects into “ ectoblasts ” and “ entoblasts,” and woul 
similar objection to Mayer’s views, since in weevils ( Attelabus), abun- 
dantly proved by Dr. Le Conte to be the oldest of Coleoptera (a fact 
ignored by Dr. Mayer, whose genealogical tree of Coleoptera represen" 
the antiquated classification of this order), we demonstrated that the 
primitive band is external, while in Telephorus it is internal, though ou" 
1 Embryological Studies on Hexapodous Insects. Memoirs of the P eabody 
Academy of Science, 1872, p. 15. 
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