EXPERIMENTS ON ARTHROPODS 107 



innervate the five gills which are located on the 

 abdomen of the animal. If the whole central nervous 

 system with the exception of these ganglia be removed, 

 the rhythmical respiratory activity continues un- 

 changed. Immediately after the operation, which is 

 accompanied by a great loss of blood, the respiration 

 may be interrupted for an hour or more. If we touch 

 the gill-plates during this time, the stimulation occa- 

 sions a series of rhythmical respiratory movements 

 which, however, soon cease. After a time, the gills 

 begin their respiratory activity again spontaneously, 

 and are only interrupted by an occasional cramp. 

 This interruption of the respiratory movements is also 

 found occasionally in the normal Limulus, where, if it 

 remains quiet, the respiratory movements may cease 

 for an hour or more. At this place we will not go 

 into details concerning this phenomenon. 



The abdominal ganglia are thus centres for the 

 automatic movements of the abdominal gill-plates. 

 All the gills move in the same phase. It is probable 

 that the inspiration begins with the first gill and ex- 

 tends to the following gills in succession, but rapidly 

 enough to make the whole appear simultaneous. Ac- 

 cording to the prevailing opinions, we should be 

 obliged to assume from this either that only one, for 

 instance the first, of the four abdominal ganglia, is 

 automatically active, and that the rest are stimulated 

 from this, or that, if each of the four ganglia is 

 rhythmically active, a common centre of coordination 

 exists somewhere in the four ganglia. If we sever 



