152 A. J. CARLSON. 



pericardium and the heart, the slender filaments reaching the 

 dorsal and posterior side of the heart along the suspensory liga- 

 aments. The nerves that are given off from the thoracic 

 ganglion near the roots of the first ambulatory nerves (2) take a 

 dorsal direction through the opening between the second and the 

 third endosternites and pass ventral and lateral to a greater bulk 

 of the flexor muscles than is the case of the anterior pair. On 

 reaching the extensor muscles the nerves run posteriorly on their 

 surface, ventral to the anterior nerves, and at the level of the 

 anterior end of the heart each nerve gives off a small branch (8) 

 to the plexus of arteries and suspensory ligaments at the anterior 

 end of the pericardial cavity. In very large specimens the nerves 

 can be followed along the suspensory ligaments to the dorsal 

 side of the heart. 



The other nerves from the dorsal surface of the . thoracic 

 ganglion (3 to 6) turn dorsally through the openings of the sub- 

 sequent endosternites and ramify, with the arteries, on the flexor 

 and extensor muscles that are situated dorso-laterally in the tho- 

 racic cavity. I could not trace any of their branches to the 

 heart, nor does stimulation of these nerves effect the heart. 

 That the two anterior pairs of nerves really send fibers to the 

 heart is further shown by stimulation of these nerves. The an- 

 terior pair contains inhibitory, the second pair accelerator fibers. 

 In Callinectes Connant and Clarke found that the inhibitory fibers 

 reach the heart in the recurrent cutaneous nerves (/r;/.). This is 

 not the case in Palinnrus. Branches from the posterior rami of 

 these nerves can be followed close up to the pericardial cavity, 

 but not on to the heart itself, or on to the suspensory ligaments, 

 and in no instance did stimulation of these nerves effect the heart. 

 The course of the cardiac nerves in the plexus of suspensory lig- 

 aments and small arteries in and surrounding the pericardiac 

 cavity is not easily made out, because the nerves, the arteries 

 and ligaments have nearly the same color and transparency. 



10. The Arachnids.- -To the recent paper on the innervation 

 of the heart of Liumliis by Patten and Redenbaugh (1899) I have 

 only one item to add, viz., the connection of the inhibitory 

 nerves with the heart. The heart and the heart -nerves of this 

 interesting arthropod are shown in Fig. 23. The ganglion cells 



