122 Desci'iptions of Preparations. 



collar in which a part of the pharynx is still left. Upon either 

 side of the pharynx a reticulation of g-anglionic masses may be seen 

 with a lensj one of which masses is much larger than the rest, and 

 running parallel with the commissural cords is connected with 

 them by six or more nerve branches. Two distinct strands may 

 be distinguished in the anterior portion of the ventral cord, and 

 they are underlaid by a continuous stratum of vesicular substance, 

 which at intervals is aggregated into more or less distinct ganglia, 

 from each of which a pair of nerves is given off on either side, 

 whilst a single nerve is given off on each side from the portion 

 of the cord interposed between each two pairs of ganglia. These 

 latter nerves may probably be considered as homologous with the 

 nervi transversi of the Arthropoda, and as serially homologous with 

 the branches of the plexus already described as existing upon the 

 pharynx. They are given off in each segment anteriorly to the 

 paired nerves, and take a course outwards in relation with the 

 posterior aspect of the anterior dissepiment of each segment. They 

 are accompanied by a branch from the sub-neurally placed pseud- 

 haemal vessel, whilst the paired nerves are similarly accompanied 

 by a branch from one of the pseud-haemal vessels on either side of 

 the nerve cord. The ventral cord takes the shape of a thick band 

 in which the ganglionic enlargements are difficultly recognizable 

 for a space corresponding with that occupied by pharynx oeso- 

 phagus and reproductive organs ; posteriorly to the fifteenth seg- 

 ment it becomes much slenderer, but the ganglia become much 

 more distinguishable, though separated by wide interspaces up to a 

 point a little way posterior to the middle of the entire length of 

 the body. Finally, for a length nearly equal to that of the pos- 

 terior half of the animal, the cord becomes much more distinctly 

 moniliform, its ganglionic enlargements being very plainly marked 

 though very closely apposed. The terminal ganglion of the chain 

 is, contraiy to what is seen in some other Annelids, as also in many 

 Arthropoda, smaller than those which precede it. The ganglia do 

 not maintain the same numerical equality with the segments in 

 other Annelids as in Lumbricus, exceeding their number in some, 

 as Aphrodite, and falling below it in others, as Hirudo, see Preps. 

 41, 42. The two rows of paired setae are well seen on either side 

 of the middle line ; the inner setae in the two segments fifth and 

 sixth in order anteriorly to the clitellus are seen together with the 



