THE BRACHIOPODA. 29 



along, that side of the body from which the other lobe of the 

 mantle proceeds ; and then either ends, blindly, in the middle 

 line (Fig. 10), or else terminates in a distinct anus between the 

 pallial lobes. 



The principal ganglionic mass is situated behind and below 

 the mouth, in the re-entering angle between the gullet and the 

 rectum ; in other words, the intestine has, as in the Polyzoa, a 

 neural flexure (Fig. 10). In all Brachiopoda which have been 

 carefully dissected a singular system of cavities and canals 

 situated in the interior of the body, but in free communication 

 with the surrounding medium, has been discovered. This, 

 which I shall term the " atrial " system (from its close corre- 

 spondence with the system of cavities, which has received the 

 same name in the Ascidians), has been wrongly regarded as a 

 part of the true vascular system, and the organs by which it is 

 placed in communication with the exterior have been described 

 as " hearts." There are sometimes two and sometimes four of 

 these " pseudo-hearts," situated in that part of the body wall 

 which helps to bound the pallial chamber. Each pseudo-heart 

 is divided into a narrow, elongated, external portion (the so- 

 called " ventricle "), which communicates, as Mr. Hancock has 

 proved, by a small apical aperture with the pallial cavity ; and 

 a broad, funnel-shaped inner division (the so-called " auricle "), 

 communicating on the one hand by a constricted neck with the 

 so-called " ventricle," and, on the other, by a wide, patent 

 mouth, with a chamber which occupies most of the cavity of 

 the body proper, and sends more or less branched diverticula 

 into the pallial lobes. These have been described as parts of 

 the blood vascular system ; and arterial trunks, which have no 

 existence, have been imagined to connect the apices of the 

 ventricles with vascular networks of a similarly mythical 

 character, supposed to open into the branched diverticula. 



In fact, as Mr. Hancock has so well shown in his splendid 

 and exhaustive memoir, published in the Philosophical Trans- 

 actions for 1857, the true vascular system is completely distinct 

 from this remarkable series of " atrial " chambers and canals, 

 the function of which would appear to be to convey away 

 excretory matters and the products of the reproductive organs, 



