igog.] F. H. Stewart : Investigator sicarius. 289 



The lateral nerve cords issue one from each dorsal ganglion. In the head they 

 are closely apposed to the wall of the pharynx (text-fig. i). The only ventral com- 

 munication between them consists of a single fine commissure in this region. 



In the neck (pi. xxi, fig. 5) they lie on the ventral side of the coronal diaphragm 

 in the angle formed by this structure and the body- wall. This is also their situation 

 in the region of the trunk (pi. xxi, figs. 6, 7, 9). Throughout the greater part of 

 their course they are separated ventrally by |-th of the circumference of the body, 

 dorsally of course by f ths. 



At the level of the anus they curve inward and toward the dorsum over the 

 nephridia and gain the cœlomic surface of the respiratory chamber, lying at about 

 the junction of the ventral and the two lateral quadrants of that organ (pi. xxi, fig. 

 9, r.c.n.). In this situation they run forward to the anterior extremity of the respira- 

 tory chamber and here join in a broad commissural band (pi. xxi, fig. 8). 



It should be noted that throughout this part of their course, although they are 

 actually in front of the anus, they are morphologically posterior to it, since the res- 

 piratory chamber is an introverted postanal portion of the body. More particularly 

 still it should be noted that the commissure connecting the two cords lies dorsal as 

 well as posterior to the anus. This subject will be further discussed below. 



The situation of the lateral nerves relatively to the body- wall is worth notice. 

 They lie throughout their course internal to the muscular layers and just external 

 to the cœlomic epithelium. Compare this condition with that in Priapulus and Hali- 

 cryptus. Of the latter two Scharfï [6] writes ' the nervous system lies entirely in the 

 ectoderm ' and ' all previous observers state that the nervous system lies immediately 

 under the hypodermis, between it and the annular muscles. In reality, however, it 

 is placed within the hypodermis, the ganglionic cells being simply modified hypoder- 

 mic cells and the fibrils their processes.' Investigator has evidently advanced consider- 

 ably in the evolution of its nervous system beyond the members of these two genera, 



its nearest allies. » 



Reproductive System. 



The only specimen which was suitable for minute examination proved to be a 

 male. 



The single testis (pi. xxi, fig. 7) consists of an elongated cellular mass running 

 for the whole length of the trunk in the dorsal line, to the left of the alimentary canal. 

 It is contained within a membranous endothelial tube which is presumably a com- 

 partment of the ccelom. At its anterior end the walls of this tube are in continuity 

 with the walls of the dorsal blood-vessel and of the vessels of the alimentary plexus, 

 and throughout its course the dorsal blood-vessel runs in its dorsal wall. 



On reaching the level of the anterior extremity of the respiratory chamber it curves 

 inward to the axial line of the body, towards the base of the gill-stalk (pi. xxi, fig. 8). 

 At this point unfortunately my series of sections is slightly torn and it has not been 

 possible to clearly demonstrate an opening from the testicular tube into the respira- 

 tory cavity. It seems almost certain, however, from the course taken by the organ 

 that its contents escape to the exterior through this cavity. 



