228 K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 



as well as their glandular system in general, then will not neces- 

 sitate us to place them higher than the Articulata. It would 

 be almost as one-sided to raise all these above the Mollusca, 

 although in general the greater variety in their vital manifesta- 

 tions might give them a fair claim to such a position.** Funda- 

 mentally, however, each of these sections of the animal kingdom 

 has its own standard, which can only be determined by its type. 

 The greater the histological and morphological differentiation, the 

 higher, according to our view, is the perfection in the same type. 

 A less morphological differentiation is, however, always an ap- 

 proximation to the fundamental type. Thus, the Annelida, on 

 account of the similarity of their limbs, appear to us to be of 

 lower organization, notwithstanding their vascular system, whose 

 limitation in Insects is readily comprehensible, as a consequence 

 of the development of their tracheae. For us the Myriapoda do 

 not stand much higher, their manducatory instruments being 

 true cephalic feet and their head being but little separated 

 from the other almost identical rings. In the Thysanura and 

 Parasita a greater morphological differentiation has arisen. 

 And the structure of the true Insects is in them, as it were, 

 sketched out. 



Just as gradual modifications of the Annulata may be re- 

 cognized through Myriapoda, Thysanura and Parasita, so may 

 such be observed through the Isopoda, Amphipoda and Stoma- 

 poda to the Decapoda, and through the Scorpionidae to the 

 Arachnida. 



For what reason, hov/ever, the proper Spiders, or the Decapoda 

 among the Crustacea, are to be reckoned as more perfect than 

 the true Insects, is not clear. On account of their more perfect 

 vascular system ? This is only a consequence of a less active 

 interchange with the air, whose more powerful influence always 

 assists the development of animal life. 



If, on the other hand, the Individualization of the organic 

 constituents is to be our standard of perfection, we observe in 

 the Decapoda, besides the slight histological differentiation which 

 to me is obvious, a tendency to compress the organs of sense, 

 the motor and the plastic organs, into one chief centre, — in con- 

 sequence of which the type is greatly modified, but its essential 

 parts become little separated ; in the Arachnida the plastic body 



