XVII THE HEART 473 



chonella, and others ; but according to Joubin/ 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 Crania neither the large canal nor the 

 small canal communicates with the general body cavity, but he 

 admits that in Lingida 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 JValdheimia venosa, and recently Blochmann 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 



^ "Recherches sur I'Anat. ties Brachiopodes Inarticiiles," Arch. Zool. Exp. (2), 

 Tome iv., 1886. 



- Unterstichuncjen liber den Bau der Brachiopoden, Jena, 1892. 



^ " Vorlaufige Mittheilungen liber Bracliiopoden," Xool. Anz. Bd. viii. 1885. 



