Miscellaneous. (i 
only with that portion of the circulatory apparatus which is contained 
in the abdomen, that is to say with the heart and the vessels which 
open into or issue from it. 
The heart of the mason Mygale greatly resembles that of the rest 
of the spiders. Enveloped by a pericardium it is situated in the 
dorsal portion of the abdomen, immediately beneath the integument. 
Its anterior region is attenuated to form the aorta, which penetrates 
into the peduncle and passes on to ramify within the cephalothorax. 
Its posterior portion exhibits a corresponding diminution in size, and 
then terminates with a bifurcation. In transverse section it is not 
circular, but shows an angle in its lower part, since the heart is as 
it were carinate on its inferior face. Four pairs of lateral 
eminences are to be observed upon this organ. The anterior pair, 
which correspond to the curvature of the heart, are but slightly 
marked ; the following pair, which I shall call the intermediate ones, 
are much more prominent, as are also the third (median); finally 
the posterior pair, situated near the extremity of the heart, are much 
less pronounced. Lach of these eight eminences is perforated by an 
aperture, forming a communication between the pericardiac cavity 
and the interior of the heart. There are accordingly four pairs of these 
apertures, while the Araneida Dipneumones only possess three pairs, 
and less in a few very rare cases. The number four has, moreover, 
been stated by M. Blanchard for Mygale Blondu. The anterior 
apertures are placed at the sides of the heart; the intermediate ones 
are a little further advanced towards the dorsal face ; and, lastly, the 
median and posterior pairs are almost entirely dorsal, and in these 
cases the two apertures of the same pair are separated one from 
another, in the median line, only by a somewhat narrow strip of 
tissue. Like the corresponding eminences, the intermediate and 
median apertures are much more developed than the anterior, and 
above all than the posterior pair. The two edges of each aperture 
are constituted by powerful bundles of muscular fibres, which 
sharply define them. 
According to M. Blanchard, the heart of Mygale Blondii is divided 
into five chambers. In the mason Mygale this division into 
chambers does not exist, any more, in fact, than in the Araneida 
Dipneumones. On examining the interior of the heart, we observe 
that the two lips of each aperture are turned back in such a way 
as to make a noticeable projection on the inside of the heart when 
they are applied together. ‘The internal angles of the two apertures 
of the same pair are only united together, on the interior of the 
organ, by a slightly projecting raphe, which is produced by the 
muscles which encirele these orifices; on the floor of the heart a 
similar seam is even much less distinct. The arrangement here 
described is that of the intermediate and median apertures; it is 
even much less pronounced in the case of the anterior and posterior 
ones. Neither do we find the valvular folds, which, according to 
Dugés, should conceal the origins of the vessels. The heart therefore 
forms only a single chamber, “exhibiting four enlargements. 
As regards the vessels, Dugés confines himself to stating that 
Ann. & Mag. N. Hist. Ser. 6. Vol. xii. 6 
