230 DISCOVERY REPORTS 



the body wall giving off branches which enervate both the dorsal longitudinal and the 

 circular muscles (Fig. 9). The combined posterior cardiac and pericardiac nerve then 

 continues downwards to enter the swelling on the ventral chain that I have already 

 described (Fig. 13). 



The main interest of this cardiac system is the correspondence between it and the 

 supposed method of functioning of the body musculature which I have deduced from 

 purely morphological grounds (pp. 215-216). 



There are two antagonistic sets of muscles which may be termed the protractor and 

 the retractor systems of the body. The protractor system consists of the dorsal longitu- 

 dinal and circular system of the dorsal body wall of the trunk. By their contraction, 

 as I have explained (p. 195), the anterior body centring round the adductor muscle 

 will be protruded forwards. The retractor system consists mainly of muscle 10 which, 

 since it is attached directly to the adductor tendon, will pull back the anterior body. 

 In addition, muscles 4, 5 and 1 1 will retract the massive second antennae. Obviously 

 the interaction of these two sets of muscles not only brings about the movement of the 

 body relative to the shell, but as a resultant controls the internal body pressure, that 

 is the blood pressure. Further, in this, as in all forms, the efficient working of the heart 

 depends on a nicely balanced blood pressure. Now in the heart itself there is the single 

 cardiac neurone which is connected through the cardiac nerve directly to the nerves 

 controlling, on the one hand, the protractor, on the other the retractor system of 

 muscles. This suggests at once that the single cardiac neurone is the controlling centre 

 regulating the balanced action of these two sets of muscles. 



Further, for the heart beat a continual supply of blood is necessary, and this enters 

 the pericardium mainly via the efferent canal. This canal is kept open by the contraction 

 of the bowed muscles, dorsal longitudinal nos. 6, 7 and 8 (p. 215) and, in correspondence 

 with this, the posterior cardiac nerve can be traced to nerve endings on these muscles 



(Fig- 9)- 



BASAL GANGLION SYSTEM 



The series of basal ganglia which I described in Doloria (Cannon, 193 1, p. 468) as 

 occurring in the base of each limb is present also in Gigantocypris (Plate XLI, fig. 5). 

 The ganglia are large — so large that it is possible to dissect them out of the limbs, with 

 the exception of the last trunk limb. Here the ganglion is so small that it was only with 

 difficulty that it was discovered as an elongated accumulation of nerve cells near the 

 base of the limb. Apart from this the basal ganglion system calls for no comments. 



VISCERAL SYSTEM 



The visceral system is extremely well developed. It is based on the same plan as 

 that of Doloria, but in addition there is a new system connected with the aorta. 



The labral loop bearing the medial labral ganglion is present (Figs. 11, 16). Its two 

 ends emerge from the nerve ring in the same position as in Doloria, that is, in the 

 mandibular region (see p. 226), but there are no marked mandibular swellings. 



