CASTLE: NORTH AMERICAN RHYNCHOBDELLID. oi 
Their ventral capsules show the following modification in arrangement ; 
they have been displaced from the typical tandem position to a side-by-side 
position (Figures 8, 10; compare Figure 9, somites XXIX.—XxxXIII.). 
The lateral capsules of ganglion No, 2 are found dorsal to the pharyngeal sac 
(2, 2, Figures 8, 12). They seem to have been displaced backward to a po- 
sition somewhat posterior to the lateral capsules of ganglion No. 3 by a migration 
in that direction of the supra-csophageal commissure (Figure 8 ; compare 
Figures 11, 21). The commissure in this species is normally thrust back of 
the position in which it is shown in Figure 8, so that it lies about over the 
lateral capsules of ganglion No. 5. The animal whose brain is represented in 
Figure 8 was curved ventrad so that the commissure was thrust forward of its 
usual position and the row of lateral capsules below it was straightened out 
a little. The position of the ventral capsules of ganglion No. 2 is shown in 
Figures 8 and 10; the nerve root (11., Figure 8) arises at the anterior end of 
the brain just ventral to nerve root I. 
The ganglionic capsules of neuromere No. 1 all lie dorsal to the pharyngeal 
sac and anterior to the supra-cesophageal commissure (Figures 8, 12). I be- 
lieve that the most anterior and ventral of these (1v., Figures 8, 12), which 
lies closely attached to nerve root I. in each half of the body, is homologous 
with a ventral capsule of one of the succeeding ganglia, Capsule rv. extends 
out lateral to, sometimes even ventral to, nerve root I., so that its end may 
appear in sections between nerve roots I. and It. 
Oka (94) states that he finds in the brain of “Clepsine” (Glossiphonia) 
always thirty nerve capsules, and he accordingly regards it as equivalent to 
five fused ganglia and no more. Since G. stagnalis was one of the species 
studied by him, I am unable to understand how he can have reached such a 
conclusion, unless he has overlooked altogether the capsules of somite 1. which 
lie anterior to the supra-cesophageal commissure. 
Both the number and arrangement of the nerve capsules, and the number and 
position of the nerve roots, show clearly that in G. stagnalis stx fused ganglia are 
represented in the bran, and that in the entire body THIRTY-FOUR somites are 
represented. 
(2) Somite Limits. 
It remains to explain the grounds on which the limits of the somites have 
been placed by me as indicated in Figure 4. Whitman (’85) pointed out 
many years ago that a certain ring (the first, according to his account) of each 
typical somite in the body of a leech is more richly supplied with sensory 
organs (“‘sensille ”) than any other ring of the somite. In many species of 
Glossiphonia special color markings or papille are also found on the sensory 
ring. Color markings, however, are wanting in G. stagnalis, and the sen- 
sillxe are not sufficiently conspicuous in the living animal to make identification 
of the sensory rings at all certain. But a carmine stain of the proper intensity 
renders identification of the sensory rings quite easy by giving them, especially 
along the margins of the body, a somewhat darker color. Observing this fact, 
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