XVII THE HEART 473 



ehonella^ and others ; but according to Joubin,i it communicates 

 in Crania at one point with the tentacular canal. It is probably 

 originally a part of the body cavity. Blochmann^ states in very 

 definite terms that in Crayila neither the large canal nor the 

 small canal communicates with the general body cavit}^ but he 

 admits that in Lingula the small canal opens into that space. 



The Circulatory System 



The details of the discovery of the central circulatory organ 

 of Brachiopods form a curious and instructive chapter in the 

 history of modern morphological inquiry. Hancock, in his 

 monograph on the group, described and figured on the dorsal 

 surface of the alimentary canal a well-developed heart, which 

 had been previously noticed by Huxley, who first showed that 

 the organs which up to his time had been regarded as hearts 

 were in reality excretory organs. In connexion with this heart 

 Hancock described numerous arteries, distributed to various 

 parts of the body. The observers who have written upon the 

 anatomy of Brachiopods since Hancock's time, in spite of the 

 fact that they had at their disposal such refined methods of 

 research as section cutting, which was quite unknown at the 

 time his monograph was written, have almost all failed to find 

 this circulatory system, and many of them have been tempted 

 to deny its existence. Blochmann,^ however, in the year 1885 

 stated that he had found the heart, and had seen it pulsating in 

 several species of Brachiopoda which he had rapidly opened 

 whilst alive. Joubin has also described it in large specimens 

 of Waldheimia venosa^ and recently Bloclimann has published a 

 detailed account of his work on this subject. Both these authors 

 describe the heart as a vesicle with muscular walls, situated 

 dorsal to the alimentary canal. From this, according to Bloch- 

 mann, a vessel — the branchio-visceral of Hancock — runs forward 

 as a triangular split in the dorsal mesentery supporting the 

 alimentary canal. This vessel divides into two at the oeso- 

 phagus, and passing through some lacunae in the walls of this 



1 "Recherclies sur I'Auat. des Bracliiopodes Inarticules," Arch. Zool. Exp. 

 (2), Tome iv., 1886. 



2 "Untersuchungen iiber den Ban der Brachiopoden," Jena, 1892. 



3 "Vorlaufige Mittheilungen iiber Brachiopoden," Zool. Anz. Bd. viii. 1885. 



