434 HYDE. [VoL. IX. 
During such an operation the animal loses much blood and 
is left very weak, and since it can no longer swallow food, it 
cannot be strengthened. 
Immediately following the operation, the respiratory acts 
may stop for an hour or more. A touch, however, on either 
the gill-plates or carapace will arouse the activity for a short 
interval. After a few hours the plates begin to move spon- 
taneously, and only occasionally is their rhythm interrupted by 
cramp or cessation of movement. 
One animal lived three days after the operation, and was 
then subjected to the post-mortem. 
In another Limulus the whole brain, post-oesophageal gang- 
lion, and all but three ganglia of the collar were extirpated. 
The three ganglia were left, so that the animal could be fed and 
kept alive. To my satisfaction, the animal lived three weeks 
after the operation. During all of that time the respiratory 
activity continued quite normally; at times there were intervals 
of cramp or interrupted respiratory movements, but after a 
while, the gill-plates spontaneously began their regular rhythm 
again. 
The experiments have therefore proved, beyond all doubt, 
that the respiratory movements of Limulus can continue when 
only the abdominal cord is left; furthermore, that the centre 
of the respiratory movements is not located either in the brain, 
oesophageal collar, or post-oesophageal ganglion. 
E. Experiments on the Abdominal Cord and its Ganglia. 
(a) The abdominal cord was cut through, just anterior to 
the operculum (O Fig. 1). Thus the connection between the 
brain and the cord is destroyed. In such an animal a few 
hours after the operation, periods of about seventy-five seconds 
of slow respiratory movements alternate with periods of about 
sixty seconds of complete cessation. 
The day following the operation, intervals of slow respiration 
alternate with intervals of cramp movements, as the following 
observations indicate ; — 
