PROGRESS OF MICROSCOPICAL SCIENCE. 95 
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 external openings. In framing 
hypotheses like these, one guess may be as good as another. 
“ The author, in a footnote, 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,’ 
u. 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 Memoir 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 homo- 
logues of the legs is emphasized. 
“ As regards the position of the primitive band of insects, Mayer 
ignores the remarks of Dr. Dohrn on its significance in classification, 
and considers that the circumstance whether the primitive band is 
external or floats within the yolk is of much importance, laying down 
the law that ‘insects with an external primitive streak are in general 
older than those with an inner. We have previously * objected to 
Dohrn’s classification of insects into ‘ ectoblasts’ and ‘ entoblasts, and 
would make a similar objection to Mayer’s views, since in weevils 
(Attelabus), abundantly proved by Dr. Le Conte to be the oldest of 
Coleoptera (a fact ignored by Dr. Mayer, whose genealogical tree of 
Coleoptera represents the antiquated classification of this order), we 
demonstrated that the primitive band is external, while in Telephorus 
it is internal, though our observations are called in question by 
Dr. Mayer, who, however, so far as we know, has never published 
any observations on the embryology of this or any other animal, the 
entire essay being based on facts observed by previous writers. 
“ While the essay is interesting and suggestive, the leading idea, 
that hexapodous insects first appeared as winged organisms and not 
as larval forms, will, we think, be found to have no valid foundation. 
We should with as much reason derive the acalephs from an ancestral 
free-swimming medusa, and not from a hydra-like form, or the 
Amphibia from the tailless rather than the tailed forms, views with 
which we imagine few zoologists would agree.” 
* “Embryological Studies on Hexapodous Insects,” ‘Memoirs of the Peabody 
Academy of Science,’ 1872, p. 15. 
