78 DR. T. DAVIDSON ON RECENT BRACHIOPODA. 



dorsata. It is always necessary to give the characters oi c species from its adult condi- 

 tion, noting the changes its apophysary system undergoes during the different stages in 

 its development. 



In 1845 Dr. Philippi described, under the name of Terebratula lupimis, a young smooth 

 examjjle of Terebratella dorsata, in which the dorsal valve still 'detains the elevated 

 Magasella septum. The type is preserved in the Berlin Museum. Philippi did not 

 figure his so-termed species, and I am indebted to Prof. E. v. Martens for a series of 

 excellent figures of the species (PI. XIV. figs. 20 a, h, 21 a). 



In 1833 Prof. Owen described, with great care and minuteness, the soft parts of the 

 animal in the sjiecies under description. He says that " the arms and viscera, as in 

 Lingttla, are inclosed between the lobes of the mantle, which are precisely adapted to the 

 inner surface of their corresponding valves, and are in such close contact with them as to 

 require great care in separating the valves from them. That lobe of the mantle which 

 corresponds to the perforated valve, is traversed longitudinally by four large vessels ; the 

 opposite lobe is similarly traversed by two such vessels. . . . The margins of the mantle 

 are thickened . . . the marginal cilia are so minute as only to be perceptible by means 

 of a lens. At the posterior part of each of the lobes the expanded fleshy extremities of the 

 muscles are seen ; those which were attached to the perforated valve being nearer the 

 hinge by their whole length, than the anterior pair of the opposite valve. Each of tlie 

 oval muscular disks is composed of an anterior larger muscle and a posterior smaller one. 

 Through the transparent mantle may also be seen the green-coloured follicular liver 

 intervening between and stirrounding the muscles, and the folded ciliated arms." Prof. 

 Owen then describes at some length the great arterial trunks, adding that " The size of 

 these vessels at once suggests their subserviency to other purposes than that of merely 

 returning the blood necessary for the nutrition of the mantle. . . . Corresponding to the 

 large branchial veins there appear under the microscope much smaller vessels, which I 

 regard as the branchial arteries ; these run parallel with the middle of the branchial 

 veins, and terminate in the margins of the mantle from which the veins commence. 

 These margins present the following appearances when viewed with a high magnifying 

 power : — they are puckered at regular distances, the puckering being apparently caused 

 by the insertions of delicate cilia, which pass as far within the mantle as they project 

 beyond it ; in the interspaces of the cilia the margin of the mantle is minutely fringed : 

 and within this fringe is a canal, which extends itlong the whole circumference of the 

 lobe, and from which the branchial veins appear to take their origin : the marginal canal 

 is contracted where the cilia are inserted into it, which gives it a sacculated appearance, 

 like that of the canal of Petit in the human eye. The uniform results of repeated obser- 

 vations on aU the specimens of Terebratula wliich I have had at my disposal, convinced 

 me that the vascular mantle was the chief, if not the sole respiratory organ ; and the 

 utility of the marginal cilia in reference to this function can now be readily appreciated, 

 in consequence of the discovery of the i-emarkable property which cilia possess of 

 exciting determinal currents in the surrounding water." 



After having stated so much. Prof. Owen then describes the shape and double attach- 

 ment of the loop, and adds, " the interspace between the two folds of the calcareous loop 

 is filled up by a strong but extensile membrane, which binds them together, and forms a 



