K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 19? 



I need follow out this remark no further ; any closer examina- 

 tion will be rendered superfluous if I succeed in clearly explain- 

 ing what I mean by type. 



The type then is the relative position of the parts. It may be 

 readily recognized that the different types are modifications of 

 certain archetypes {Haupt-Typen), in which this relative position 

 is especially characterized, and that intermediate forms occur 

 which either unite the characters of the archetypes into a middle 

 type, or in which one archetype preponderates in the one half of 

 the body, in the other another. For the present I leave these 

 intermediate forms out of consideration, referring to the essay 

 which I have cited. But I must once again bring forward the 

 archetypes in this place. 



I believe that four archetypes may be clearly demonstrated, — 

 the peripheral or radiate archetype, the articulate or longitudinal 

 archetype, the massive or molluscous archetype, and the arche- 

 type of the Vertebrate*. 



The peripheral type is exhibited by certain discoid Infusoria, 

 by the Rhizostomidae, Medusae and Asteridae. In their external 

 form superficial dimension is represented. The principal anti- 

 thesis is that of centre and periphery. The contrast of ingestion 

 and egestion lies in a direction from the centre to the circum- 

 ference. Hence the whole organization radiates from a centre. 

 Besides this, the contrasted relation of upper and lower sides 

 only is developed, and this slightly ; no distinction of right and 

 left, or of anterior and posterior, exists at all. Their movements 

 are thence without definite direction. As the whole organization 

 radiates from a centre, so the centres of all the organic systems 

 are in the middle, or are disposed circularly around the middle 

 (thus the stomach is in the middle, and round it are the nerves 

 and vascular circlets, when these parts are developed at all) ; 

 from them branches pass into the radii. In every radius is 

 repeated what exists in any one ; and every radius, if we follow 



* I will not attempt to decide here, whether a peculiar type is not to be 

 recognized in those animals whose whole organization is disposed not round a 

 central point, but round an axis, as in the Holothuria. Ingestion and egestion 

 are not here contrasted as centre and periphery, but as two ends of a line 

 around which the remaining organization is peripherally disposed. Here too 

 as a lower grade the Nematoidea might be arranged, and perhaps other lower 

 forms. 



