1)1^ T. DAVIDSON ON llECEXT BEACHIOPODA. 21 



al)iuplly about. The oesophagus also becomes dimly delined. lu the third stage the 

 peduncular segment is developed and projects from the posterior portion of what can 

 now be called the thoracic segment. At this stage the embryo either remains immovable 

 upon tlie bottom of the dish or slowly moves about. In two cases delicately barbed 

 setae to the number of thirty-five projected directly backward from the peduncular 

 segment. The embryo is still clothed with cilia, though the long pencil of cilia has 

 disappeared. The head is closely drawn to the thoracic segment, whicli becomes Avider 

 in transverse diameter, so as nearly to hide -the peduncle. In the fifth stage the thoracic 

 ring commences to fold, or turn iipward upon opposite svirfaces of its circumference, so 

 as to gradvially enclose the head ; one fold being made slightly in advance of the other 

 represents the larger or ventral valve. In this stage appear clusters of barbed and 

 deciduous setge upon tlie anterior margin, and in a later portion of this stage the first 

 hardened areas of the dorsal and ventral plates make their appearance, and the cirri 

 appear as bkinted papillae about the mouth. In the sixth stage the shell becomes 

 rounded, the peculiar scaled structure makes its appearance, and the formation of tubules 

 perforating the shell and of permanent setse takes place." Tlie author adds, further on, 

 " that the eggs not only fill the large pallial sinuses, but liang in clusters from the 

 genital band ; from these parts they escape by dehiscence, and float freely in the 



perivisceral cavity The eggs ai'e not uniform either in shape or size." Prof. 



Morse then describes in detail each of the stages ; but space will not allow me to 

 proceed further with his elaborate investigations, as they would demand numerous 

 illustrations. (See Plate V. figs. 1-31.) 



Dr. Gwyn Jeffreys states, in vol. ii. p. 7 of his ' British Conchology,' that in the fry-stage 

 the little creature can creep and swim ; but, " After quitting the embryonic state, they 

 become invariably and permanently fixed to other substances, being incapable of any 

 other motion than making a half turn round the peduncle or pivot." 



Mr. Lucas Barrett, who had an opportunity of examining T. caimt-serpentis in life, 

 says*: — "This species shows more of itself than any other, and protrudes its cirri 

 further ; it was met with everywhere [near the coast of Norway], in small numbers, 

 iu 30 to 150 fathoms, often attached to Oculina. The cirri on the re- j,j„ g 



fiected part of the arms are shorter than those on the first part, as shown /^ 



in the woodcut. The cirri were almost constantly in motion, and / \ 



often observed to convey small particles to the channel at their base, '!; 



When placed in a small glass of sea-water, the valves gradually opened. 

 Individuals remaining attached to other objects manifested a re- 

 markable power and disposition to move on their pedicles. Detached y. ccnrnf-.ta-jjcitix, 

 specimens could be moved about without causing the animal to "^"1- L. Barrett, 

 close its valves. If any of the protruded cirri were touched, the cirri were retracted 

 and the valves closed A\itli a snap, but soon after opened again. When the oral 

 arms are retracted the cirri are bent up, but are gradually uncoiled and straightened 

 when the shell is opened, before which the animal has often been observed to prntrude 



* Ann. & Mag. Nat. Hist. 2nd ser. vol. xvi. p. 2.57, 1855. 



