60 Transactions of the 



water vascular system. The remarkably anomalous condition of 

 the alimentary canal of Mermis seems to stand between the condi- 

 tion seen in Ascaris, and that in Tenia, Echinorhynchus, &c. 



The lateral bands present histological elements precisely similar 

 to those described by Olaparede * in the ventral cord (Bauchstrang) 

 of the earth-worm, about the nervous nature of which there can, I 

 think, be no doubt whatever. These are accurately figured by 

 Schneider, f 



Each lateral band is divided into two, longitudinally, by a well- 

 marked raphd of fibrous tissue, and a central canal may be seen on 

 either side of the raph^. This may be clearly observed in a trans- 

 verse section. The greater part of the band consists of fine fibrous 

 tissue, minute oil-globules, and small corpuscles, called by Claparede, 

 in the earth-worm, connective tissue nuclei. Besides these, there 

 are numerous larger scattered ganglion corpuscles, just as there 

 are in the ventral cord of the earth-worm. I have distinctly 

 traced the connection between these and the nerve filaments. The 

 whole band is invested by a delicate layer of epithehum, exactly as 

 that of the earth-worm is. 



In the earth-worm the ventral cord terminates in a ganglionic 

 ring round the pharynx ; % in Ascaris the lateral bands terminate 

 in a similar ganglionic ring. 



The pharyngeal ring gives ofi" a thick band of similar struc- 

 ture to each of the lips, which terminates in four large lobes. 

 Posteriorly the ring gives ofi" several short tapering bands, identical 

 in structure with the lateral bands. These are soon lost in the 

 tissues. Occasionally one or both lateral bands split before joining 

 the ring. Nerves are given ofi" at intervals from either side of the 

 lateral bands, which may be traced running transversely to the 

 muscular layer, and ramifying in the integument. 



Schneider§ has clearly seen and described this nervous ring in 

 Ascaris megacephala, and has figured the lateral nerves given ofi" 

 from the lateral bands ; || but he has failed to trace the connection 

 between the lateral bands and the ring, and describes the nerves as 

 coming from a nerve-trunk in the interior of the lateral bands. I 

 suspect this has arisen from his method of treating his preparations 

 with acetic acid, and from the fact, that the longitudinal nerve- 

 fibres, which form chiefly the nerves, are situated in the centre of 

 each half of the lateral bands ; whilst the commissural fibres and 

 ganglion cells are scattered over their periphery. 



With regard to the nature of the axial canals in the lateral 

 bands, I confess I am ignorant. I have a strong suspicion that 



* E. Claparede, ' Zeitscbrift fiir Zoologie,' band xix., p. 563. 

 t ' Monograpbie der Nematoiden.' % Claparede, loc. cit. 



§ 'Monograpbie der Nematoiden,' and in 'Mull. Arcbiv.' 1856. P. 1. 

 )1 'Monograpbie der Nematoiden.' 



