94 INTERNAL ANATOMY OF INSECTS. 
opacity of the head rendered it impossible to ascertain 
the mode of anastomosis. An excurrent and returning 
current were also traced to each of the legs a . But the 
phenomena of the circulation was most distinctly visible in 
the larva of Ephemera vulgata, even more distinctly than 
it is possible to trace it in the larvae of frogs and newts. 
In this animal the circulation, with the help of the micro- 
scope, is at once visible in the three last segments of the 
body; and with a little attention is discoverable not only in 
the three terminal cauduhe, and in the upper joints of the 
legs, but also in the head, and particularly the roots of 
the antennae. In the posterior part of the body there 
are on each side two currents of blood, not bounded by 
parietes, situate on each side of the intestinal canal, the 
inner one being the most considerable. The external 
one communicates with the internal by several interme- 
diate branches ; from this probably the streams are de- 
tached, which in the form of loops are seen at the upper 
joints of the legs, though it is not possible precisely to 
ascertain this, nor even whether these lateral currents 
continue distinct in the thorax, which probably they do. 
At the ninth abdominal segment these currents which 
flow posteriorly from the head, change their direction, 
and are inflected so as to enter the pulsating heart, from 
which the current again flows towards the head. Before 
they enter the heart they give oft' three streams, one for 
each of the three caudulcc. The currents in these caudulce 
present the phenomena of the circulation with peculiar 
distinctness, and are particularly remarkable from the 
circumstance, that the excurrent and recurrent streams, 
though closely approximated without any visible sepa- 
a Introd. to Comjt. Anat. ii. 39o — . Engl. Trans. 
