432 TLD EE. [VoL. IX. 
nerves supply the first five gill-plates, whilst the sixth pair 
goes to the anal region. The anterior pairs of nerves go to 
the integument and give off fibres that run forward and unite, 
forming on each side a lateral longitudinal nerve. These nerves 
are known as the lateral nerve chains. 
The respiratory movements in Limulus consist in a consecu- 
tive dropping and raising of the gill-plates, respectively known 
as the inspiratory and expiratory phases. The former consists 
of a rhythmical dropping of all the gill-plates from the ventral 
abdominal wall; at the same time the gill-books (Fig. 4) become 
fully dilated and their contents of blood thoroughly exposed 
to the water. The expiratory phase consists, first, of a quick, 
consecutive, upward beat of the gill-plates against each other 
and the ventral wall; second, a slight forward pressing of the 
posterior margins of the plates. During these stages the gill- 
books are first flattened, then slightly compressed against each 
other, and at the same time their contents are forced out. 
A normal Limulus makes on an average twenty-seven inspira- 
tory movements a minute, when the temperature of the water 
is about 24° C. I often noticed that when normal Limuli lie 
motionless the movements cease for an hour or more; that is, the 
gill-plates remain in the expiratory phase, then, for no apparent 
cause begin spontaneously to move in their regular rhythm. 
Moreover, in normal Limuli, occasionally, and always after an 
operation of some part of the nervous system, one can see a 
peculiar, respiratory activity or cramp-like movement of the 
gill-plates. A better understanding of this is gained from 
Fig. 3, which gives the position of the plates during the 
movement. 
I. LoOcALIZATION OF THE CENTRE OF RESPIRATORY 
MOovEMENTS. 
A. Experiments on the Brain. 
The investigation was begun by performing various opera- 
tions on the brain and noting their effects. It may be said 
here that the results of these experiments warrant the conclu- 
sion, that lesion or loss of part or the whole brain (anterior 
