198 K. E. VON BAER. -PHILOSOPHICAL FRAGMENTS. 



it up to its centre, takes a similar share in the central parts also 

 (the urinary system alone appears to make an exception), so that 

 the whole body may be divided into a number of similar sectors, 

 and the loss of a ray, so long as the middle remains uninjured, 

 does not disturb life, since none of its necessary component 

 parts are wanting. 



In the longitudinal type, which obtains in the Vibriones, Fi- 

 laria, in Gordius*, in the Naida, and in the whole Articulate 

 series, the contrast of ingestion and egestion is relegated to the 

 two extremities of the animal, and thus gives a character to the 

 whole organization; the mouth and the anus are at the two 

 ends, and in general the sexual organs also, yet at times these 

 have their apertures more anteriorly. This is more frequently 

 the case with the female organs, which are not merely egestive, 

 but are also ingestive, than with the male organs. When the 

 organs of both sexes are removed from the posterior extremity, 

 the aperture of the female organs generally is placed more for- 

 ward than that of the male organs. It is thus in the Myriapoda 

 and the great family of Crustacea ; the Leech and the Earth- 

 worm form a rare exception. With the fixed position of the 

 anterior extremity, as the ingestive pole, the organs of the senses 

 as instruments for the receptivity of the nervous system early 

 attain a considerable grade of development. 



So long as the type remains unchanged, the intestinal canal 

 passes straight through the body. It is the same with the vas- 

 cular and nervous systems. Every organic movement then has 

 this principal direction, only subordinate branches pass off 

 laterally; especially when the principal character is repeated 

 along the whole length, as in a galvanic battery, so that every 

 separate segment possesses its own anterior and posterior ex- 

 tremity, together with its portion of the essential constituents of 

 the organism. 



Thence the disposition to break up into many portions in the 

 direction of the length of the body. In the true Insects pos- 

 sessing metamorphosis, these articulations are united again into 

 three principal sections, in the first of w ? hich the nervous, in the 

 second the motor, and in the third the digestive life predomi- 



* If these animals, or some of them, are not perhaps in accordance with the 

 previous note, to be brought under one type with the Holothuriadae. 



