THE BRACHIOPODA. 27 



we shall find, nevertheless, a singular fundamental resemblance 

 of internal structure to the latter. All known Polyzoa are com- 

 pound animals, that is to say, the product of every ovum gives 

 rise, by gemmation, to great assemblages of partially indepen- 

 dent organisms, or zooids. The Brachiopoda, on the contrary, 

 are all simple, the product of each ovum not giving rise to others 

 by gemmation. All the Brachiopoda possess a bivalve shell — a 

 shell composed of two, more or less horny, or calcified, pieces, 

 which are capable of a certain range of motion on one another, 

 and are very commonly articulated together by teeth and sockets. 

 The proper body, which is small when compared with the 

 size of the shell, has its dorsal integument produced into broad 

 membranous expansions, which line the interior of the valves of 

 the shell, and are called the lobes of the mantle, or " pallium." 

 The aperture of the mouth is situated in the middle line, between 

 the pallial lobes, and, on each side of it, is a longer or shorter 

 prolongation of the body, provided with ciliated tentacula. It 

 is from the presence of these " arms " that the class has received 

 its name. The tentaculate oral disk of a Plumatella is already 

 horse-shoe shaped (Figs. 7 and 8) ; suppose each eras of the 

 horse-shoe to be pulled out to a much greater length, and 

 tentaculated "arms" would be produced, closely resembling 

 those of the Brachiopoda. 



The mouth leads into a gullet which is directed towards, or 

 lies along, that side of the body from which one lobe of the 

 mantle, the anterior, is continued ; the gullet opens into a 

 stomach, provided with a well-developed liver ; and from the 

 stomach., an intestine proceeds, which is directed towards, or 

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

 mantle proceeds ; and then either, as I pointed out some years 

 ago,* ends, blindly, in the middle line (Fig. 9), or else ter- 

 minates in a distinct anus between the pallial lobes. 



* Professor Owen, in the second edition of his lectures on the " Comparative 

 Anatomy and Physiology of the Invertebrate Animals," published in 1855, thought 

 it not unbecoming to sneer at this discovery. " There may be blindness somewhere, 

 but I think not at the termination of the intestine of Terebratula." — L. c, p. 403. 

 As my statements have subsequently been fully borne out by Mr. Albany Hancock 

 and by M. Laeaze Duthiers— two of the best minute anatomists of the day— T trust 

 Mr. Owen is now fully satisfied as to where the " blindness" really was, in 1855. 



