Circulation of Body Fluids 551 



ishes, and when all of the longitudinal nerves are transected coordination 

 between the anterior and posterior ends ceases. 



The hearts of some insects are neurogenic. Two chains of nerve cells 

 occur on the heart of the cockroach,^' ^^^ and these probably are pace- 

 makers.'^* In Aeschna, cells from the cardiac ganglion appear to have mi- 

 grated to part of the stomatogastric system.-'** Maloeuf'-^-* failed to find nerve 

 cells in preparations of hearts of larval Anax and adult Belostovta, which 

 beat normally so long as dorsal suspensory ligaments connected the heart to 

 the body cuticle. Similarly in Agrion and Hydrophilus cutting of the alary 

 muscles stops the heart, and nerve cells are said to be absent from the heart 

 of Bomhyx (Kuvana, in Maloeuf'^*). The innervation of insect hearts is 

 summarized by Mclndoo;'^^ nerve cells are found in the hearts of several 

 adults and nymphs (bee, cockroach and others) but are absent from hearts 

 of larvae (army worm). Pharmacologically the hearts of the cockroach 

 Blatta, the grasshopper Melanoflus, the cricket Stenopehnatus, and the hon- 

 eybee behave like the hearts of Crustacea and of Limulus, in that they are 

 accelerated by acetylcholine. '•^'^' ^* The hearts of larval wax moths Galleria 

 are not afifected in rate or form of electrocardiogarm by acetylcholine.'*' It 

 is probable that insect hearts are unusually sensitive to tension and may not 

 beat unless extended; it is also probable that most adult insect hearts are 

 neurogenic, although the pacemaker cells may have migrated outside, and 

 that some larval hearts may be myogenic. The hearts of spiders are appar- 

 ently neurogenic.'*^** 



Among the annelids nerve cells have been described in the hearts of Areni- 

 cola^^' and Lumhrictis;'^^^' these hearts contract by a layer of smooth muscle. 

 Nerve cells were not seen in Nereis (Neanthes), in which the contractions 

 are due to endothelium and Rouget-like cells.'^*^- *^^ The beats of Arenicola 

 and Lumhricus hearts are accelerated by acetylcholine'^*^ (Fig- 210); it is prob- 

 able that they are neurogenic. Distention by blood is important in the es- 

 tablishment of contractions.'" 



In the hearts of ascidians nerve cells have been seen in Ciona^ and Mol- 

 gula,^^ but not in Salpa.''-^^' ^^^ The beat normally originates at the ends of 

 the heart, although Hunter^^ found that middle pieces in Molgida nianhat- 

 tensis contracted for some time after isolation. In Ascidia atra^^' ***' and Pero- 

 phora viridis^^^ the beat is for a time in one direction (abvisceral) and then 

 for a number of beats in the opposite direction (advisceral). Normally the 

 two ends are pacemaker regions. '^*^ Acetylcholine accelerates in Peropho- 

 ^Q 199, 157 although it is relatively ineffective in Ciona. A rise in tempera- 

 ture accelerates the heart by the same amount, irrespective of the end at 

 which the beat originates.-*''^ The incomplete evidence available indicates 

 that the hearts of ascidians, at least of Molgula and Perophora, are neuro- 

 genic. 



Lymph hearts of Amphibia (frogs and toads) and fish (eel) are normally 

 under control of the spinal cord. The pacemaker characteristics in frogs and 

 toads have been well summarized.'^'^'^' ^^^ When the connections of the anu- 

 ran lymph heart to the spinal cord are transected the heart usually stops for 

 a few minutes, and then beats spasmodically, the beat later becoming co- 

 ordinate and rhythmic. Anterior and posterior homolateral hearts are normally 



