186 K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 



first type that the principal vascular trunks are tubes, and a 

 true sharply defined heart appears only very late in the already 

 modified form of the Decapoda. In the radiate type we have 

 rings united by a perpendicular vessel. In the molluscous type, 

 in which there is a general tendency to the formation of vesicles, 

 the central point of the organization naturally appears earliest as 

 a distinct heart. The French zoologists then are greatly in 

 error in regarding the Mollusca from this organ alone as more 

 highly developed than the Insects, and in placing the Acephala 

 above the Bees. 



Finally, this idea enables us to comprehend how the general 

 form of the type depends upon the productive conditions (zeu- 

 genden momenten), W 7 hile the inner development depends espe- 

 cially upon the nature of the animal. Perhaps these considera- 

 tions may be profitable if they be kept in view in the course of 

 investigations into the course of development. 



II. On the Development of Animals, with Observations and Re- 

 flections. By Dr. K. E. VON BAER, Konigsberg, 1828. 



[Ueber Entwickelungs-Geschichte der Thiere, von Dr. K. E. VON BAER. 

 4 to, 1828.] 



THE FIFTH SCHOLIUM. On the relations of the forms which 

 the individual takes in the different stages of its development, 

 pp. 199-264. 



1. The prevalent notion, that the embryo of higher animals 

 passes through the permanent forms of the lower animals. 



The relation of the forms which the embryo gradually assumes 

 has already been referred to in its proper place in the course of 

 the exposition of the mode of development of the chick. The 

 importance of the subject, however, and the interest with which 

 it has lately been regarded, lead me to think it fitting and ne- 

 cessary to undertake a special investigation of these relations, 

 since they appear to me to be somewhat different from what the 

 general opinion represents them. In order to be clearly under- 

 stood in developing my own views, and to bring forward more 

 distinctly their essential features, I must be permitted first to 

 explain the prevalent mode of conceiving the progress of the 

 development of the embryo. 



Few expressions of the relations of organized beings have met 



