668 DK. H. CHAELTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



upon the subject. Latterly, however, I have been able to confirm the accuracy of 

 Schneider's statements in every particular, and have no longer the shadow of a doubt 

 that the similar structures which we have both recognized in these and other Nematoids 

 do constitute the most important portions of a nervous system. 



The difficulties besetting the proper recognition of this system are, however, extreme, 

 owing to the intimate and confusing manner in which it is mixed up with a blending of 

 processes from the lateral and median lines, and a multitude of offshoots from the 

 neighbouring muscles. 



Schneider has detailed very fully the different parts of the nervous system as they 

 exist in A. megalocephala, and as I have myself recognized them in individuals of the 

 same species ; so that I shall describe as briefly as possible what I have made out in the 

 nearly allied species A. lumbricoides, and one or two other members of the same genus. 



The best method for preparing the nervous system for examination in either of these 

 animals is that recommended by Schneider, and is as follows : — Select if possible a rather 

 young specimen, on account of the greater transparency of its tissues, cut off a portion 

 about ^" in length from the anterior part of its body, and having previously settled which 

 is the dorsal median line*, insert the point of a fine scissors within the cut extremity of 

 the oesophagus, and then slit open this, together with the body wall, in the mid-dorsal 

 region. The head lobes may be either cut off or left The posterior comers of the 

 opened body wall should now be pinned out whilst the oesophagus is being carefully 

 stripped off". The specimen should then be boiled in dilute acetic acid for about two 

 minutes, after which the thick cuticle may generally be stripped off, and finally the 

 preparation should be mounted in glycerine to make it still further transparent. When 

 saturated in this fluid the preparation will bear considerable pressure without injury, 

 and so often enable ganglion-cells and their issuing fibres to be better detected. 



In A. lumbricoides the nervous ring (Plate XXIV.) which constitutes the most 

 marked portion of this system is situated about -jxj" from the anterior extremity, and is 

 about -3x3" in breadth. It merely surrounds the commencement of the oesophagus, but 

 is not closely adherent to it, though it is almost inseparably connected with the parietes 

 of the body. It seems to embrace the oesophagus somewhat obliquely, the dorsal portion 

 being nearest to the anterior extremity. The method of its connexion with the body 

 wall may be best seen in transverse sections (Plate XXVI. figs. 1 & 11), when a fibrous 

 ring is recognized with more or less nucleated ganglion-cells interspersed, dinded into 

 four equal portions by its contact and blending with developments from the lateral and 

 median lines. Also it is intimately connected with the four great longitudinal muscles 

 by means of fibres passing to and blending with it in the intervals between its other 

 attachments. These muscular prolongations passing to the nervous ring may be con- 

 sidered as the most anterior representatives of those processes, which throughout most 

 of the body posterior to this situation have a transverse direction, and are attached to the 



• This may always be known by its having a single head lobe opposite its termination, instead of itself termi- 

 nating between two, as is the case with the ventral line. 



