G. E. Beecher — Development of the Brachiopoda. 137 



pedicle at this stage is also defined, being a modification of the 

 caudal segment. It may serve to attach the larva to foreign 

 objects, as in Cistella, figure 10, and Terebratulina, or it may 

 remain undeveloped for a time as in Glottidia and Discinisca. 

 A rudimentary digestive tract is present. 



9 10 



Cistella neapolitana Scacchi. 



Figure 9. — Xeoembryo. Completed cephalula stage. 



Figure 10. — Typembryo. Transformed larva resulting from folding upwards of 

 mantle lobes over cephalic segment : ad, muscles from bundles of setse to 

 sides of body cavity; di, muscles from dorsal to ventral sides of body; vp, 

 muscles from ventral side of body to caudal segment or pedicle. (9, 10, after 

 Kovalevski.) 



The body muscles which have been developed thus far 

 consist of four distinct pairs. Two pairs lie close to the sides 

 of the body cavity, and extend to the points of insertion of the 

 bundles of bristles, figure 10, ad. They become after transfor- 

 mation the four adductor muscles of the valves. The third 

 pair extends from the ventral side of the body to the caudal 

 segment, and is converted into the ventral pedicle muscles, 

 figures 10, 15, 16, vp. The fourth pair is situated posterior to 

 the digestive tract, and extends from the dorsal to the ventral 

 wall of the body, figure 10, di. They form the divaricator 

 muscles in the mature brachiopod, figure 16, di, and are 

 divided into or duplicated by a pair of dorsal and a pair of 

 ventral divaricators. There is also a pair of dorsal pedicle 

 muscles in the larva of Liothyrina and Terebratulina. 



The folding upwards of the mantle lobes forms the first 



