MOLLUSCOIDA : BRACHIOPODA. 3 I 5 



the pseudo-hearts are regarded as oviducts, and it is stated 

 that they have been found to contain mature ova, so that 

 there can be little doubt but that this view of their nature is 

 the correct one. By Rolleston the pseudo-hearts are looked 

 upon as corresponding with the so-called " organ of Bojanus" 

 of the Lamellibranchiata. 



The function of respiration is probably performed, mainly, 

 if not entirely, by the cirriferous oral arms, as it appears chiefly 

 to be by the homologous tentacular crown of the Polyzoa. A 

 true vascular system and a distinct heart are present in some, 

 at any rate, of the Brachiopoda, but this subject is still involved 

 in considerable obscurity. In Terebratula the heart is in the 

 form of a unilocular, pyriform vesicle, placed on the dorsal 

 surface of the stomach. 



The nervous system consists of a principal ganglion of no 

 great size, placed in the re-entering angle between the gullet 

 and the rectum. In those Brachiopods in which the valves of 

 the shell are united by a hinge, the nervous system attains a 

 greater development, and consists of a gangliated cesophageal 

 collar. 



The sexes are said to be ordinarily distinct, but in some 

 cases they appear to be united in the same individual. The 

 development of the Brachiopoda is still shrouded in consider- 

 able obscurity, but in some cases the young have been observed 

 to move from place to place, either by protruding their ciliated 

 arms, or by means of spines developed in the ventral lobe of 

 the mantle. As regards the development of Terebratulina 

 septentrionalis, the changes observed by Mr Morse show the 

 close affinity which subsists between the Brachiopoda and the 

 Polyzoa. The arms, namely, in this species commence as a 

 series of ciliated tentacles placed round the mouth, most strik- 

 ingly similar to the lophophore of such a Polyzoon as Pedicellina. 

 The lophophore becomes horse-shoe-shaped, and the "arms" 

 are finally produced by the growth and development of the free 

 ends of the horse-shoe. 



The Brachiopoda may be divided into two groups, called 

 respectively the Articulata and Inarticulata. In the former 

 the valves of the shell are united along a hinge-line, the lobes 

 of the mantle are not completely free, and the intestine ends 

 cascally. In this group are the recent Tcrebratulida and Rhyn- 

 chonellidce. In the Inarticulata the valves of the shell are not 

 united along a hinge- line, the mantle-lobes are completely free, 

 and the intestine terminates in a distinct anus. In this group 

 are the Craniadce, Discinidcz, and Lingulida, 



AFFINITIES OF THE BRACHIOPODA. There can be no ques- 



