PHYSIOLOGY OF THE INVERTEBRATE HEART. I 55 



nection with the nerve-cord, in some specimens there appears to 

 be connections only at the level of the second pair of ostia, in 

 others the connection is made in the middle of the third seg- 

 ment, while in some the main, if not the only, connection is the 

 one just behind the third pair of ostia. 



It is rather difficult to homologize the cardiac innervation of 

 the crustaceans with that of Limulns. In the crustacean heart 

 the ganglion cells are not congregated in a single ganglion on 

 the surface of the heart, but scattered throughout the muscle. 

 There appears, however, to be this homology that in the crusta- 

 cean heart the ganglion cells are massed particularly at the pos- 

 terior end of the dorsal wall of the heart. In Pali minis the 

 cardiac nerves take their origin from the anterior end of the 

 thoracic ganglion, the abdominal ganglia not making any connec- 

 tions with the heart ; in Limulns the cardiac nerves take their 

 origin from what actually corresponds to the thoracic ganglion 

 and from the abdominal ganglia as well. This difference is 

 probably due to the fact that the Limulns heart retains its 

 primitive elongated character while the crustacean heart is very 

 much shortened and confined to a small space in the cephalo- 

 thorax. 



Regarding the innervation of the heart in insects we have the 

 observations of Miiller and Brandt (quoted by Kolbe, 1893) that 

 the heart and the aorta is innervated from the second pair of 

 oesophageal ganglia. This cardiac nerve would thus seem to 

 correspond to the " cardiac nerve of Lemoine " in the crustaceans, 

 which, as we have already pointed out, appears not to have any 

 basis in fact. To my knowledge no connection between the 

 abdominal ganglia and the heart analogous to that in Limulus 

 has been traced in the insects. 



Dogiel ( 1877) has described ganglion cells on the heart or in 

 close proximity of the heart of the larva of Corcthra plumicornis. 

 According to Lang (1900) a nerve or nerve-cord on the dorso- 

 median side of the heart similar to that in Limulns has been 

 described in some of the myriapods (Pcripatus, Jules}. 



ii. The Tunicate s. Despite numerous researches with the 

 view of finding nerve cells and nerve fibers in the heart of the 

 tunicates the results have been, until a recent date, uniformly 



