Ill 



Ascidia, consisting of a single elongated cavity, and not composed of 

 a distinct auricle and ventricle as in the ordinary Bivalves," and he 

 compares the hearts of Brachiopoda to the auricles of Area, &c. 

 (Trans. Zoological Society, vol. i. p. 159). 



In 1843, however, M. Vogt's elaborate memoir on Lingula ap- 

 peared, in which the true complex structure of the ' heart ' in this 

 genus was first explained and the plaited ' auricle ' discriminated 

 from the ' ventricle; ' and in 1845, Professor Owen, having apparently 

 been thus led to re-examine the circulatory organs of Brachiopoda, 

 published his ' Lettre sur 1'appareil de la Circulation chez les Mol- 

 lusques de la Classe des Brachiopodes,' in which he felicitates 

 M. Milne-Edwards on the important confirmation of the views which 

 the latter entertains with respect to the lacunar nature of the circu- 

 lation in the Mollusca, afforded by the Brachiopoda, and describes 

 each heart of the Terebratulidse as consisting of a ventricle and a 

 plaited auricle, the pallial veins not terminating in the latter but in 

 the general visceral cavity. As the Professor does not recal the view 

 which he had already taken of the circulation in Orbicula, I presume 

 that he considers two opposite types of the circulatory organs to ob- 

 tain in the Brachiopoda, the direction of the current being from the 

 mantle through the heart towards the body in Orbicula, and from 

 the mantle through the body towards the heart in Terebratula. 



The possibilities of nature are so various that I would not venture, 

 without having carefully dissected Orbicula, no opportunity of doing 

 which has yet presented itself, to call this view in question, but I 

 think it seems somewhat improbable. Indeed the structural rela- 

 tions which I have observed and which are described below, do not 

 appear to me to square with any of the received doctrines of Bra- 

 chiopod circulation, but I offer them simply as facts, not being 

 prepared at present to present any safe theory on the subject. 



In Waldheimia flavescens there are two ' hearts,' situated as Pro- 

 fessor Owen describes them, but so far as I have been able to ob- 

 serve, the ventricle cannot be described as an ' oval ' cavity, inas- 

 much as it is an elongated cavity bent sharply upon itself. Hastily 

 examined of course this may appear oval. I have been similarly 

 unable to discover ' the delicate membrane of the venous" sinuses,' 

 which is said by Professor Owen to " communicate with and close 

 the basal apertures of the auricles," or to perceive that the auricular 



