308 GENERAL SUMMARY TO 



of the valves. The cilia lining the cirri produced gentle currents in the water. In this 

 position, with the valves widely open and cirri expanded, the animal will remain motion- 

 less for twenty or thirty seconds, and then, with an abrupt closing of the valves, suddenly 

 assume its first position. In watching these motions for a long time, one could not 

 help being impressed with the fact that caution was evidently indicated in the slow and. 

 careful movements made in elevating and opening the shell, while the prompt closing of 

 the valves and the alert manner in which the animal regained its first position seemed 

 to show that food had been secured and further caution was unnecessary." 



Dr. Gvvyn Jeffreys 1 writes -. — In the fry-stage the little creature can creep and swim, 

 but after quitting the embryonic state it becomes invariably and permanently fixed to 

 other substances, being incapable of any other motion than making a half turn round 

 the peduncle or pivot. This is so with respect to the Terebratulidce? 



The development of Lingula has been minutely and ably described by Prof. W. K. 

 Brooks. He alludes to Prof. J. McCrady having given a brief description (from memory) 

 of the swimming larvae of Lingula, without tracing in detail the transformation into 

 the adult. 3 Prof. Brooks says that the free-swimming embryos of Lingula pyramidata, 

 Stimpson, are met with in great abundance at Fort Wool from about the middle of 

 July to the middle of August ; that the changes undergone by the larva during develop- 

 ment are gradual, and do not involve any marked metamorphosis. " The larva is 

 enclosed between two orbicular flattened valves, which are not articulated to each other, 

 but are free around the entire circumference. The dark -coloured, somewhat opaque, 

 flask-shaped digestive organs occupy the centre of the cavity of the shell, and are in 

 contact above and below with the integument which lines the valves. Around the 

 digestive organs is a body-cavity bounded externally by the integument, which is con- 

 tinuous with the mouth above and below, and is bent downwards at right angles to the 

 valves to form the body-walls. On the sides of, and behind, and in front of the body, 

 there is a capacious mantle-chamber, which is open around the entire circumference. 

 The mouth opens in the centre of a broad, flat, nearly circular disk or lophophore, around 

 the margin of which are the ciliated tentacles. The plane of the lophophore is not at 

 right angles to the long axis of the body, but inclined so as to be nearly parallel to it. 

 The tips of the tentacles may be extended beyond the edges of the valves and thus form 

 a swimming apparatus, like the velum of a mollusk, by the aid of which the larva floats 

 in the water or rises slowly to its surface." 



1 Brit. Conch., vol. 2, p. 7, 1863. 



2 For many useful details see also Balfour's 'Treatise of Comparative Embryology,' vol. i, 1831. 

 8 A notice of a larval Brachiopod, ' Proceedings of the Elliott Soc. of Nat. Hist, of Charleston.' 



