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 caudulcz, 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 caudultf. 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 Comp. Anat. ii, 395 . Engl. Trans. 



