No. 3.] STUDY OF STENOSTOMA LEUCOPS O. SCHM. 287 



dahlia (i : 10,000) the brain becomes of a light purple color. 

 Under these circumstances two nerve bands stained like the 

 brain may be seen to run backward from the posterior end of 

 each ganglion. The other tissues are not stained. 



An outer very narrow and short band (Fig. 16, S.N) runs from 

 the dorsal side of the posterior end of each ganglion to the dish- 

 shaped organs, and an inner much longer nerve band may be 

 seen to run from each ganglion to the posterior one-half of the 

 body. These lateral nerve bands (Fig. 16, L.N) may be seen in 

 sections to run on either side of the alimentary canal a little 

 nearer to the dorsal than to the ventral side of the body. On 

 account of their very small size it is difficult in cross-sections to 

 distinguish them from the parenchyme. In longitudinal sections 

 of a budding worm these nerve bands may be seen to connect 

 the ganglia which are to form the brain of the anterior bud with 

 the ganglia which are to form the brain of the posterior bud. 

 In one of these sections (Fig. 21) the nerve bands may be seen 

 to be made up of a single layer of small cells which are long and 

 narrow, and the long axes of which are parallel with the long 

 axis of the body. They are 4 /x long and .75 [l wide. They are 

 finely granular and are provided with small oval nuclei .5 /a in 

 diameter. At a point midway between the ganglia this nerve 

 may be traced through three or four longitudinal sections 5 /i in 

 thickness, thus making the nerve at this point from 15 yu, to 20/U. 

 in width. 



Graff ('75, p. 414) says that when the worm is contracted the 

 ciliated pits are embedded in the anterior end of the lobes of 

 the brain, but when the worm is in its normal condition the 

 brain is entirely separate from the ciliated pits. 



I have not found a living worm in any state in which the 

 ciliated pits have not been embedded in the forward projection 

 of the lobes of the brain (Fig. i, C.P). Out of fifty series of 

 sections of worms in all states of contraction not one instance 

 was found in which the ciliated pits were not embedded in 

 ganglion cells which were continuous with those of the posterior 

 end of the brain. 



Graff ('82, p. 259) says that according to Schneider ('73) the 

 lobes of the brain are connected by a double commissure which 

 surrounds the water vascular system. He also states that Hallez 

 ('79), like all other workers, found but a single commissure. 



