640 THE AMERICAN NATURALIST. | [Vor. XXXVI. 
be found in a ventral but not necessarily median position. 
Also this mass is usually at a normal distance from the fused 
intestine. Morgan (1900) has noted this delay in the forma- 
tion of the pharynx when the worm is cut anterior to the 
genital pore at this time of year (July 2) and finds about 
twelve days instead of seven required for complete regenera- 
tion. His later experiments, begun July 31, gave different 
results, but this was probably due to the degeneration of the 
reproductive organs between these two dates, as he found that 
the time required for this set of pieces to become complete 
animals was only seven days. 
This delay may be due to the scarcity of parenchyma cells 
in this region, which is almost completely filled by the tissue 
of the genital organs. When these organs are fully present 
the parenchyma cells collect as shown in Fig. 6, migrating 
principally from the anterior end into the region of paren- 
chymatous tissue that lies just ventral to the penis. In this 
drawing are shown in the tissue along the edge of the geni- 
tal organs certain irregular breaks that seem to appear at 
the beginning of the degeneration of these structures. The 
pharynx forms ventral to such cavities, and the split for the 
pharynx chamber is at first entirely independent of them 
(Figs. 6, 7). Later the wall between may break down, and 
thus greatly enlarge the chamber, but if so it is a secon- 
dary process; there is also a tendency towards degeneration 
in the thin line of tissue between the pharynx and reproduc- 
tive chambers, as shown by the dotted line in Fig. 7. In no 
case, however, does the old genital pore become the new 
pharyngeal pore. 
As the genital organs degenerate, which I have found takes 
place during the last two weeks in July and the beginning 
of August, the region in which the pharynx appears becomes 
quite irregular. The only feature that seems at all constant is 
the relative distance between the cross-branch of the intestine 
and the pharynx thickening. That this is true may be seen 
by a study of its position with relation to that of the genital 
pore. The main genital duct opening to the exterior persists 
longer than any other part of these structures, but its presence 
