206 K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 



mining one, while in those which are situated posteriorly it is 

 the egestive movement. In the Holothuriadae, the Mollusks, 

 the larvae of Insects which inhale air by their hinder extremities, 

 the respiratory organs are emptied by muscular contractions. 

 The refilling is principally a consequence of the cessation of 

 muscular activity ; at least, if an antagonistic muscular action be 

 superadded, it is less than the expelling force. The reverse takes 

 place in the pulmonated animals ; the reception of air is here 

 more active, its expulsion is more passive. The inhalant passage 

 will therefore determine the position of the apparatus, not the 

 retrogressive passage of the exhaled air. Now, though we find 

 the lung double, yet in all animals the right lung is larger, and 

 in the true Ophidia it is this alone which is developed, a trace 

 only remaining of the left. To this may be added, that in some 

 Cetacea, as in the genus Physeter, the right nostril is dwarfed. 

 Indeed it may obtain even more generally that the right nasal 

 aperture is smaller than the left, as we see for example in Som- 

 mering's description of the skull of the fossil Hyaena. We may 

 then shortly indicate the course of the air in the respiration of the 

 Vertebrata by the arrow (5) in our figure (p. 238). In the gills 

 of Fishes it must be admitted that no such lateral difference is 

 apparent; but the gills are so immediately connected with the 

 animal part of the body, as the transitory gill-arches of the pul- 

 monate animals testify, that the asymmetry of the plastic body 

 cannot develope itself in them. 



When an apparatus like the digestive passes from one pole to 

 the other through the whole length of the plastic body, it cer- 

 tainly cannot send its contents always to the right side. It is 

 only to be expected, that in those sections in which the motor 

 powers are most strongly manifested, which are therefore those 

 which determine the position of the whole, the course of the cur- 

 rent will be in this direction. Now we find in all Vertebrata, so 

 far as I know, that the stomach lies to the left and the pylorus 

 to its right side, as well as the commencement of the duodenum, 

 turning to the right whether it pass at the same time forwards 

 or not. The stomach therefore propels its contents towards the 

 right side. The same relation is frequent in the muscular rec- 

 tum. Other sections must indeed pass from right to left, but 

 they are the less active. Thus I conceive that if the floor 1 in 



