K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 225 



or less downwards. Only in the Annelida is its position de- 

 cidedly, though only a little^ superior. — (p. 235.) 



p. 236. The same holds good of the cervical nervous band in 

 the Mollusca. It is not the organ which we call brain, not even 

 in the Cephalopoda, but in a manner the central part of a nervous 

 system, which, in its general relations, may be compared with 

 the plastic nervous system of the Vertebrata, but which takes 

 on a different form, inasmuch as it is not dependent upon a pre- 

 dominant brain and spinal cord. I can regard the so-called 

 brain of the Cephalopoda only as the cervical nervous band of 

 the Gasteropoda. In the former the ganglia are fused together, 

 in the latter they are more distinct. It is a centre of the plastic 

 nervous system, and can only be compared with the ganglia 

 which, in the Vertebrata, give off threads to the organs of the 

 senses and other parts of the head — here, however, possessing 

 no predominating centre, but being subordinate to the brain. 



If, in the Vertebrata, we consider the ganglion maxillare, 

 which also receives a nerve from the ear, in combination with 

 the ganglion caroticum, petrosum, Vidianum, ciliare, and the 

 threads which pass to the organs of sense and the pharyngeal 

 apparatus, we have a similar ring through which the commence- 

 ment of the digestive canal passes. 



That every portion is to be understood only by its relation to 

 the type and by its development out of it, is taught still more 

 strikingly by other parts. The tracheae of Insects are indeed 

 aeriferous organs, but not the organ which we call the trachea 

 in the Vertebrata, because the latter is a development of the 

 mucous canal, while the tracheae of Insects arise either by histo- 

 logical differentiation or by involution of the external integu- 

 ment. Sometimes the same name has been used for different 

 organs only from the want of some other word — the difference, 

 however, having been universally recognised. Thus no anato- 

 mist has regarded the wings of Insects as of the same nature as 

 the wings of Birds. In the feet, also, the essential differences of 

 the first joints have perhaps never been overlooked. A special 

 name has, with justice, been applied to the antennae. They 

 have no representative in the Vertebrata. But that they are 

 the wings of the cephalic ring is demonstrated not merely by 

 their position, but by their mode of development. They have 



SCIEN. MEM.— Nat. Hist. Vol. I. Part III. 15 



