MOLLUSCOIDA: BRACHIOPODA. 295. 



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 Lamellibraruhiata. 



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 Polyzod. 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 oesophageal 

 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 ob- 

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

 ciliated arnls, or by means of spines developed in the ventral 

 lobe of the mantle. 



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 

 caecally. In this group are the recent Terebratulidce and Rhyn- 

 chonellidcB. 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 Craniada, Discinidce, and Lirigulidce. 



Affinities of the Brachiopoda. — There can be no ques- 

 tion as to the close relationships subsisting between the Brachio- 

 poda and Polyzoa, and until recently most naturalists held that 

 both these groups had strongly-marked affinities with the La- 

 mellibranchiata. This view is still held by the generality of 

 naturalists ; but recently Mr Edward Morse has brought forward 

 evidence to show that the Brachiopoda and Polyzoa are most 

 nearly related to the Tubicolar Annelides ; and this opinion 

 liad been previously advanced as regards the latter group by 



