INDEPENDENT EFFECTOES 



57 



the attention of investigators for many years. The organ 

 itself is in the form of a swollen tube, one end of which is 

 continuous with the blood-vessels distributed to the vis- 

 cera and the other with those distributed to the gills 

 (Fig. 14). The action of the heart, the reversal of which 



B 



Fia. 14. A. Diagrammatic view of a longitudinal section of Salpa (after Herdman) 

 showing by arrows the inlet or branchial aperture and the outlet or atrial aperture as well as 

 the position of the heart h. B. Enlarged view of an isolated heart of Salpa showing the abvis- 

 ceral end g connecting with the gills and advisceral end v running to the viscera. 



was apparently first observed by Van Hasselt in 1821, 

 consists in a series of advisceral beats, by which the blood 

 is driven toward the viscera, followed by a series of ab- 

 visceral beats, by which it is driven toward the gills. The 

 relations of these sequences of beats have been exten- 

 sively studied by Schultze (1901) in Salpa, and more re- 

 cently by Hecht (1918) in Ascidia. 



It is commonly believed that in these pulsation series 

 the advisceral equal the abvisceral beats, but a closer ex- 

 amination of the facts shows that in general the ad- 



