24i M. E. Claparede on the Circulation of the Blood 



the six latter, or at least five of them (the protogiiathic artery 

 excepted), gives origin in its course to a branch which is directed 

 towards the ventral region, and empties itself into one of the 

 lacunae which w^e shall shortly describe under the name of trans- 

 verse sternal lacuna. Lastly, the artery of the protognath gives 

 origin to a branch directed upwards and inwards, and which 

 discharges itself into a blood-reservoir which we denominate the 

 median tergal lacuna. 



These are all the vessels of the cephalothorax. M. Blanchard 

 also describes, under the name of posterior aorta, a delicate me- 

 dian artery originating by one root from each secondary aorta, 

 and returning backward into the abdomen. I have not suc- 

 ceeded in seeing this, although I will not for that reason dispute 

 its existence. The Lt/coscs are certainly very unfavourable for 

 the recognition of a vessel so placed. On the other hand, 

 M. Blanchard describes neither the sternal arteries nor the 

 tergal branch of the artery of the protognath which I have 

 pointed out. I must say, however, that their investigation is 

 not free from difficulties, and that for a long time I was doubtful 

 of their existence. 



All these arterial vessels are very clearly bounded by evident 

 walls, and all present the phenomenon of rhythmic pulsations 

 synchronous with those of the heart. These pulsations, the 

 observation of which is far more easy than that of the passage 

 of the blood-corpuscles in the calibre of the vessels, greatly faci- 

 litates the study of the arterial system. The first fact that 

 strikes the eyes of the observer, whether he examines the ani- 

 mal from its lower or from its dorsal surface, is the existence of 

 two perfectly circular clear spots — one to the right, the other to 

 the left, of the median line. These spots present a very evident 

 alternate movement of diastole and systole ; they represent the 

 transverse section of the aortic crooks by the focal plane of the 

 microscope. It may indeed be easily ascertained, by an alternate 

 ascending and descending movement of the tube of the micro- 

 scope, that these circles are the expression of vertical tubes in 

 which the blood moves from above downwards. 



Reserving for future consideration the circulation of the blood 

 in the extremities, let us examine the course of the venous blood 

 in the cephalothorax. The veins here are simple interorganal 

 lacunae, without appreciable walls, into which the arteries dis- 

 charge themselves. On examining the cephalothorax from its 

 ventral surface, we soon recognize a very regular and very ele- 

 gant system of venous currents, situated immediately beneath 

 the chitinous layer. These sternal currents are almost exactly 

 rectilinear, and travel in channels existing between the muscles 

 of the sternum. We* may distinguish a median channel, a la- 



