K. E. VON BAER. — PHILOSOPHICAL FRAGMENTS. 201 



can distinguish, that is, a plastic and an animal part of the body, 

 which react mutually upon one another's form, but each of which 

 is modelled upon a different archetype. In the animal part, the 

 existence of articulation calls to mind the second archetype ; 

 ingestion and egestion are similarly referred to the two ends. 

 But there is an essential difference ; the animal part of the ver- 

 tebrate animal, namely, is not merely double on each side of a 

 longitudinal axis, but also from above downwards, and in such 

 a manner that the two inferior lateral developments enclose the 

 plastic organs, while the two superior include central organs of 

 animal life (spinal cord and brain), which are wanting in the 

 Invertebrata. The solid bony skeleton represents this type most 

 completely; from a median axis, the trunk of the vertebral 

 column, arches pass upwards, which unite in a superior crest, 

 and other arches downwards, which more or less unite into an 

 inferior crest. Corresponding with this, we have four series of 

 insertions of nerves into the spinal cord, which again contains 

 four principal cords, and a four-lobed internal gray mass. In 

 the same way, the muscles of the trunk form four principal 

 masses, as we see most distinctly in Fishes. The animal part, 

 therefore, is doubly symmetrical in its construction. 



Here, as in the essay in the ^ Nova Acta ' already cited, I will 

 not decide whether, in the course of the further development of 

 the Vertebrata, the anterior part of the animal region approxi- 

 mates more and more to the radiate archetype; I would only 

 suggest, that the brain accumulates more and more round the 

 third ventricle, and that the cerebral vessels also pass into the 

 brain from a ring, which becomes continually more and more 

 rounded, although this ring is fed by four vascular trunks, 

 as representing a relation, such, that from a type in which 

 the parts were originally arranged in fours, a radiate one is 

 developed. 



However, it appears to me to be more readily demonstrable, 

 that the type of the Mollusk predominates over the plastic part 

 of the body, although everywhere under the influence of the 

 animal part, by which the type is sometimes more, sometimes 

 less obscured. 



The plastic nervous system, as well as the peculiarity of the 

 plastic muscular system, calls to mind the molluscous type. 



