ON CLASSIFICATION. 



Second Division. NEMATONEURA (Owen).* 



(9.) In the second division of the Radiata of Cuvier, the nervous 

 matter is distinctly aggregated into filaments, and in some cases 

 nuclei of neurine, which may be regarded as rudimentary nervous 

 centres, have been noticed. It is to be lamented, however, that in 

 this most interesting group of animals, in which we have the first 

 developement of most of the organs subservient to the vital 

 functions, the extreme minuteness of some genera, and the diffi- 

 culty of distinctly observing the nervous system in the larger 

 species, has prevented our knowledge regarding their organization, 

 in this particular, from being of that satisfactory character which it 

 is to be hoped it will hereafter attain to. 



Owing to the want or imperfect condition of the nervous centres, 

 the nematoneura are necessarily incapable of possessing external 

 organs of the higher senses, the general sense of touch being as yet 

 the only one of which they are indubitably possessed ; yet in their 

 muscular system they are much more efficiently provided than the 

 acrite orders, as the developement of nervous threads of communi- 

 cation renders an association of muscular actions possible ; and 

 therefore, co-apparent with nervous filaments, we distinguish in the 

 structure of the nematoneura distinct fasciculi of muscular fibre, 

 and powers of locomotion of a much more perfect description. 



The digestive apparatus is no longer composed of canals merely 

 excavated in the parenchyma of the body, but is provided with 

 distinct muscular and membranous walls, and loosely attached in 

 an abdominal cavity. 



The circulation of the nutritious fluid is likewise carried on in a 

 separate system of vessels, distinct from the alimentary apparatus, 

 yet still unprovided with a heart, or exhibiting pulsations for the 

 forcible impulsion of the contained blood. 



The fissiparous mode of reproduction is no longer witnessed, 

 an obvious consequence of the increased complexity of struc- 

 ture, and these animals are for the most part androgynous, or 

 capable of producing fertile ova, without the co-operation of two 

 individuals. 



Among the nematoneura, therefore, we include 



* Cyclopaedia of Anatomy and Physiology. Article, ACRITA. 



