POSTURAL CONTROL OF SHELL POSITION BY ABDOMEN OF HERMIT CRAB, PAGURUS POLLICARUS .2. REFLEX CONTROL OF VENTRAL SUPERFICIAL MUSCLES

The five excitors and one inhibitor which innervate each side of the ventral superficial muscles of the hermit crab are described. The longitudinal layer receives three excitors, one of which phasically activates a lateral strip of muscle, the second tonically drives a ventromedial strip and the third innervates a strip between the other two. The inhibitor innervates the last two regions of longitudinal muscle as well as the circular muscle. Two excitors, a phasic and a tonic fiber innervates adjacent longitudinal regions of the circular muscles, but less is known of their reflex behavior. In all cases, the tonic frequency of units on the right was less than their homologues on the left, but this asymmetry was reversed during a reflex discharge. Isolation of the ganglion increased the asymmetry of spontaneous activity. It is suggested that this asymmetry may not have any functional importance but instead may be related to the different sizes of motoneurons on the two sides. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company