CONCHIFERA. 



695 



for secreting bile. Circulation is performed 

 by means of a heart generally symmetrical, 

 the ventricle of which surrounds the rectum. 

 Respiration is effected by means of four bran- 

 chial leaflets, equal in size and symmetrical, 

 arranged on either side of the body. Gene- 

 ration is simple ; the Conchifera are endowed 

 with hermaphrodism adequate to the continu- 

 ation of the species ; every individual has an 

 ovary included among the general mass of the 

 viscera. The nervous system does not form a 

 complete ring around the oesophagus ; ganglia 

 are found towards the anterior and posterior 

 parts of the animal, and lateral and very long 

 filaments form a ring within which the visceral 

 mass is included. 



Before entering upon the more particular 

 description of the organs which have just been 

 mentioned, it is essential as a preliminary to 

 institute some order among the members of 

 the class Conchifera, to throw them into a few 

 grand divisions by which the labour of de- 

 scription, in many particulars, will be very 

 much abridged. 



Lamarck divided the Conchifera into two 

 grand orders, Dimyaria and Monomyaria. 

 We are of opinion that this division may be 



preserved with some slight modifications ; and, 

 farther, that it is necessary to establish a third 

 order equal in importance to the two others, 

 and including the Brachiopoda. The ana- 

 tomical inquiries of Cuvier, and those, still 

 more recent in their date, of Mr. Owen into 

 the structure of the Brachiopoda will not allow 

 us any longer to regard these animals as per- 

 taining to the family of monomyary Conchi- 

 fers. These inquiries also prove that Cuvier, 

 in forming the Brachiopoda into a particular 

 class of Mollusca, disjoined them in too great 

 a degree from their congeners. It is from re- 

 garding both of these views as carried too far, 

 that we have been led to propose a new divi- 

 sion which to us appears to be called for, and 

 to be preferable to either of the others ; this is 

 to restore the Brachiopoda to the type of pro- 

 per Conchifera, and to establish a third order 

 of this family for their especial reception, to 

 which the title of Polymyaria might be given. 

 Instead of placing this order at the end of the 

 Conchifera, however, it appears better to set it 

 at the head, especially if the analytic method 

 of Lamarck be adopted as the basis of the 

 classification. The Conchifera we should, then, 

 propose to arrange in the following order : 



O 

 cj 



First sub-class. 



BRACHIOPODA, 

 Or POLYMYARIA 



Second sub-class, y 



DIMYAR1A "\ 



Third sub-class, 



MONOMYARIA 



f 1st sub-order: valves articulated. 

 C. 2nd sub-order : valves free. 



Order 1st. The f 1st sub-order : shell regular. 



lobes of the mantle < 



more or less united C 2nd sub-order : shell irregular. 



lst sub . order . shell regular. 



/ lobes of the mantle < 



V disjoined . . . C 2nd sub-order : shell irregular. 



ord <^ ^ foot. 



The organization of the Brachiopoda being 

 more simple than that of the other Conchifera, 

 renders it proper to place this order at the be- 

 ginning of the class. The Dimyana having an 

 organization somewhat less complex than the 

 Monomyaria constitute an intermediate order, 

 which is the most numerous of the three ; the 

 Monomyaria terminate the series. 



To facilitate the comprehension of the brief 

 descriptions which we shall give of the dif- 

 ferent parts of the Conchifera, it seems neces- 

 sary to state precisely the position in which 

 the animal must be placed in order to be suit- 

 ably observed. The animal, then, is supposed 

 to be walking before the observer, included 

 within six planes to which its different parts 

 are referred. The head or the oral aperture 

 indicates the anterior extremity of the creature. 

 This extremity is directed forwards, its pos- 

 terior extremity backwards. The back cor- 

 responds to the superior plane ; the belly and 

 foot correspond to the inferior plane, and the 



flanks of the animal to the lateral planes, one 

 of which is to the right, the other to the left. 

 The two accompanying figures (Jig. 345) will 

 suffice to give an idea of the relations of one 

 of these animals to the different planes within 

 which it is supposed to be included. 



The organization of the Conchifera is simple 

 enough. The researches of anatomists have 

 shown that these animals are provided 



! digestion, 

 circulation, 

 respiration, 

 generation, 

 and (in the greater number) 

 of locomotion; with a skin 

 or envelope common to the whole of these 

 organs ; and a nervous system bringing the 

 different systems into mutual relation with each 

 other. 



Of the organs of digestion. In the Con- 

 chifera, as among other animals, these organs 

 begin at the oral aperture. This aperture 



