K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 205 



of the heart, in order to show by it how the strong development 

 of the currents in a predominant organ may produce an opposite 

 current in a dependent part of the same system. In most ani- 

 mals the pulmonary blood flows straight backwards into the left 

 heart; where, however, this is placed in such a manner that 

 it propels decidedly towards the right side, the current of pul- 

 monary blood takes a slight direction to the left side (!'). 



So much for the direction of the arterial current. That the 

 venous current is also directed towards the right side is much 

 more obvious. The blood from the left side of the anterior half 

 of the body passes very markedly towards the right side. We 

 may therefore at once indicate the course of the venous blood 

 from the anterior part of the body by the arrow 2. That the 

 blood from the posterior part of the body also moves towards 

 the right side is shown by the deviation of the posterior vena 

 cava to the right the further forwards it passes, as well as by the 

 conformation of the intercostal trunks ; the arrow 3 represents 

 this current. It is still clearer in the portal system (4). If we 

 cast a glimpse over the whole series of animals, we find the 

 respiratory system sometimes connected with the ingestive, some- 

 times with the egestive end of the body, sometimes disposed 

 longitudinally between the two extremes. This variety of posi- 

 tion appears to be possible to the respiratory apparatus, because 

 its function is as well excretory as ingestive. One is tempted 

 to suppose that in those forms of animals in which the respi- 

 ratory apparatus occupies the anterior extremity, it acts more 

 ingestively; while, on the other hand, it is more egestive in 

 those in which it opens together with or near the intestine, as 

 in the Holothuriadae, most Mollusks, and some larva? of Insects. 

 If we extend this supposition to the changes undergone by the 

 blood itself, it must still remain hypothetical, for at present in 

 very few animals only can we determine whether the blood loses 

 or gains substance during respiration. It appears to me, however, 

 to be very clear, that in those respiratory apparatuses which are 

 placed anteriorly, the ingestive movement at least is the deter- 



compressed thorax. In animals with a flattened thorax, the heart lies more or 

 less obliquely, and in the embryonic condition sometimes more so than in the 

 adult. Thus, recently, in many embryo Hedgehogs, I found the heart directed 

 very markedly towards the left side, while it was much less so in the mother. 



