74 



tial character of ganglions on the nervous chords were not also pre- 

 sent to negative it absolutely. As the Nematoidea differ from the 

 Parenchymatous Worms by possessing a distinct nervous system as 

 widely on the one hand, as they do from the Annelida in the form of 

 that system on the other, Mr. Owen has been induced to associate 

 them with those other classes of the Radiata of Cuvier which, while 

 they are distinguished from the rest of the division by the undoubted 

 presence of nerves, agree with the Nematoidea in manifesting these 

 organs in the form of simple ungangliated disconnected chords. 



The subdivision of Cuvier's Radiata, proposed by Mr. W. S. Mac- 

 Leay, into two principal groups, the Acrita and the Radiata, may be 

 regarded as consonant with the system of nature, although the latter, 

 by the exclusion of the Nematoidean Worms, is too restricted as to 

 its contents : the definition of the former group given by its pro- 

 poser requires also modification, in consequence of the vast disco- 

 veries which have of late years been made in the organization of the 

 animals comprised in it. Mr. Owen discusses the several characters 

 assigned to the Acrita, and dwells particularly on the variations in 

 the generative system which range from gemmation and spontaneous 

 fission, observed only in this group in the animal kingdom ; to the 

 cryptandrous or productive form only, which occurs in the Cystici 

 and Cestoidea ; to the superaddition of a fecundating gland to the 

 ovary, as in Trematoda; and to the separation of the sexes, as in the 

 Acanthocephala : so as already to typify almost all the modes of ge- 

 neration by which the higher races of animals are perpetuated. 



Mr. Owen regards the molecular and the filiform condition of the 

 nervous system as respectively furnishing the primary characters of 

 the Acrita and the Radiata ; although traces of longitudinal nerv'ous 

 chords may be met with in Echinorhynchus and in the Acalephce. 

 Another distinction of great moment is the absence, in the Acrita, 

 of a distinct abdominal cavity separating the digestive cavity from 

 the parietes of the body ; the digestive cavity in those animals, what- 

 ever may be its form, being essentially a simple excavation of the 

 parenchyma. The vascular system, where traces of it are met with 

 in the Acrita, corresponds with the digestive system in being equally 

 devoid of proper parietes, and consisting of canals excavated in the 

 parenchymatous substance of the body, in which a cyclosis of the 

 nutrient fluids, analogous to that of plants, is observed, but no true 

 circulation. 



In the Acrite subkingdom, with the exception of the generative 

 and digestive organs, all the other systems are more or less blended 

 together, and the corporeal parenchyma seems to possess many func- 

 tions in common. WTiere a distinct organ is eliminated, it is often 

 repeated almost indefinitely in the same individual. Thus, in the 

 Polypi the nutritious canals are supplied by a thousand mouths ; in 



