172 MR. NEWPORT ON THE NATURAL HISTORY, ANATOMY, 
the very last period of the embryo in the ovum; since it is only in the latter periods of — 
embryonic life, when the last portion of the yelk is inclosed in the thorax of the young 
insect, and when the blood has begun to be circulated, and requires to be more exten- 
sively aérated than it has already been, that organs of respiration are formed. | 
It is exceedingly difficult to detect the existence of spiracles in the young Meloé even 
at the moment of its leaving the egg, although formed before its escape; but at the end 
of a few hours, or a day, the spiracles of the trunk become distinct, although those of 
the abdomen are still exceedingly small. With a magnifying power of three hundred 
diameters they may then be seen in specimens that have been preserved in spirit. There 
are then ten pairs of spiracles (fig. 1 bb), one pair (fig. 9) in the meso-thoracic and 
nine pairs in the abdominal segments. They are placed on the lateral margin of the 
dorsal portion of the segments on each side. The first two pairs are very much the largest, 
and are situated, the first in the anterior of the mesothorax, and the second in the first 
of the abdominal segments, the fifth segment of the body. The remaining spiracles are 
each not more than one-third the size of the three anterior ones, and are situated in the 
abdominal segments, one pair in each, from the sixth to the thirteenth inclusive. j 
The structure of the spiracle in relation with that of the tegument, at this period, is 
exceedingly interesting. The two pairs of large spiracles (fig. 9) have a circular opening, 
with a free, smooth margin, which projects from the surface, and is bounded by the edges 
of the external layer of dermal cells. The orifice of the smaller abdominal spiracles (fig. 5) 
is at first simply an irregular oval opening, or space between three dermal cells, bounded 
also by a slightly projecting margin, and very similar in appearance to the stomata on the 
surface of the leaves of plants; thus distinctly indicating, in accordance with the views of 
Schleiden and Schwann, the close analogy which exists in the mode of formation of animal 
and vegetable tissues. The two pairs of thoracic spiracles seem to be in a more advanced 
stage of development than the abdominal, but in their internal condition the whole are very 
similar. The two anterior pairs open each into a hollow, somewhat spherical cavity, or 
follicle, communicating with a sinus in the granular tissue of the segment. The diameter 
of the cavity is about three times that of the spiracle. It is narrowed at its bottom, and 
there are faint indications-of its further extension into the body. The follicles with which 
the spiracles of the abdominal segments communicate, are also much smaller than those 
of the thorax, and they are less clearly defined. A follicular cavity in the granular tissue 
of the body thus appears to constitute the earliest condition of the respiratory organ in the 
vue Meloe, and probably also in other air-breathing Articulata; since these cavities in 
Meloé are precisely similar in their general appearance to those described in my former 
memoir in the very young Stylops. They also resemble in some respects the respiratory 
organs m Sialis, which, at the moment of leaving the egg, has its abdominal branchiæ 
RA en tate gets delicate undeveloped ramifications of the tracheæ 
eic » the parietes of the cavities are lined with an aggregation of minute 
ee y Or nuclei, of rounded shape, and similar dimensions, each one measuring 
too e Rr > See radere 
BER qoi s. e cavity or follicle bounded by them is the commence- 
'achea, the lining membrane of which, formed of these cells, is 
