SUMMARY OF RESULTS. 19^ 



The vagus neuromeres are therefore the centers for important decussations 

 of impulses passing cephalad on their way from the cord to the anterior brain 

 neuromeres, v.dec. 



IV. Locomotion. 



Locomotion is normally accomphshed by coordinated walking movements 

 of the legs, or by a rhythmic beating of the legs and gills in unison, as in 

 swimming. 



I. Cutting the collar on one side, behind the hemispheres, diminishes or 

 inhibits the walking or swimming movements on the cut side. Such animals 

 walk or swim in circles, turning toward the cut side because the legs on the uncut 

 side are the most active, or they are the only ones that make any walking or swim- 

 ming movements. In water, as in air, the legs on the uncut side frequently per- 

 form the normal swimming movement, while those on the cut side are quiescent, 

 or are performing some other reflexes, as, for example, chewing. We therefore 

 conclude that the primary reflex centers for locomotion He in the last five thoracic 

 neuromeres, and for the "gill swimming" in the anterior neuromeres of the cord. 

 The secondary control centers lie in the forebrain, one on each side. 



V. Equilibrium. 



The nature of the apparatus by means of which the crab tends to right itself 

 is unknown, but apparently the part of the brain in which this function is centered 

 is near the first two vagus neuromeres. This is shown by the fact that cutting 

 across the anterior part of the collar, on one or both sides, or destroying the hemi- 

 spheres, or cutting the ventral cord behind the vagus neuromeres, does not destroy 

 the tendency, or the power, to turn the neural side down, when- free to move; 

 while the cutting, or removal, of the vagus neuromeres does destroy this tendency. 



VI. Respiration. 



The Respiratory Mechanism. — There are two distinct sets of respiratory 

 muscles, an adductor and an abductor for each abdominal appendage a.bm. 

 and e.bm.; and a large compound muscle, the branchio-thoracic, or hypobranchial, 

 attached by separate slips to the bases of all the branchial appendages. (Fig. 

 77,5, b.th.m. and Fig. 114.) 



The abductors extend from the haemal entapophyses to the anterior wall, 

 and the adductors from the entapophyses to the posterior wall of the branchial 

 appendages. The branchial muscles are supplied by motor branches from the 

 branchial nerve; the sensory branches supply an elaborate system of free nerve- 

 ends, f.e., temperature, b.L, and other sense organs, distributed over the surface 

 of the appendage. 



The motor neuromeres for the branchial muscles form three groups, two 

 on the anterior haemal, and one on the posterior haemal side of the corresponding 

 ganglion to the branchial nerve. (Fig. 62, H'"'"'^') 



