BRACHIOPODA, 703 



Fossil Brachiopoda, Zittel, Handbuch der Palaeontologie, Abth. i, Palaeozoo- 

 logie, i. p. 641 Davidson, ' British Fossil Brachiopoda,' Palaeontographical Society, 

 i-vi. 1853-1886 ; vol. vi. is a Bibliography. Life-history of Spirifer levis, Williams, 

 Amer. Journal of Science, xx. 1880. 



Bathy metrical and Geographical Distribution, Davidson, ' Report on Brachio- 

 poda,' Challenger Reports, i. 1880. 



Extension of arms, Morse, Amer. Journal of Science, xvii. 1879; Habits of 

 Lingula, Id. ibid. xv. 1878. 



Circulatory system, Blochmann, Z. A. viii. 1885. 



Development of Argiope, Shipley, op. cit. supra ; of ditto with others, Kowalew- 

 sky (abstract in French with a few figures), A. Z. Expt. (2), i. 1883. See also 

 Balfour, Comp. Embryology with authorities cited, i. p. 257. 



VERMIFORMIA. 



This group contains only a single marine genus, Phoronis, with 

 several species. It occurs on our own coasts in societies of separate 

 individuals. The animal inhabits a fixed leathery tube within which it 

 can move. It has a long body or stem, really an out-growth of the 

 ventral surface, the true dorsum being represented by a short line joining 

 the mouth and anus. The latter lies in the centre of the concavity of 

 a horseshoe-shaped disc or lophophore, which bears a series of ciliated 

 tentacles supported by a mesoblastic skeleton, and surrounded at the 

 base like that of Phylactolaematous Polyzoa by a calyx or thin membrane. 

 The youngest tentacles are the two nearest the dorsal median line, in 

 the concavity of the lophophore. The mouth is overhung by a valve or 

 epistome, the remains of the larval praeoral lobe. The nervous system 

 lies in the ectoderm. It is concentrated in two places ; as a circumoral 

 ring following the line of the tentacles, and as a cord which runs down 

 the left side of the body. Two ciliated sensory pits lie one on either side 

 the anus. The alimentary canal is ciliated and divisible into an oesophagus, 

 a first stomach, a second stomach, which is a * small strongly ciliated 

 chamber at the spot where the canal bends on itself in the body/ and an 

 intestine. The coelome, which is an archenteron, is divided into an 

 anterior and posterior part by a septum which crosses the lophophore from 

 one side to the other at the level of the nerve ring. The anterior part 

 is therefore small. The posterior is subdivided into three longitudinal 

 chambers, which communicate at the base of the body, by three me- 

 senteries, one median connecting the outer aspect of the digestive tract in 

 its whole extent to the body-wall, the other two extending laterally from 

 the stomach only to the body-wall. There is a vascular system consisting 

 of two longitudinal trunks, one of which divides in the median dorsal 

 region, and forms a ring lying at the base 9f the tentacles into each of 

 which a caecal vessel passes. An outer ring is connected to these same 



