EMBRYONIC AND LARVAL HISTORIES 69 



while the most important adult organs are formed 

 anew from the paired bands of mesodermal cells, 

 which become segmented into the hollow coelom sacs 

 of the young worm. 



Fig. 15. Diagram of Annelid Trochosphere, seen from the right side. 

 m. mouth ; an. anus ; al. gut ; ap. apical sense organ ; r. preoral 

 ciliated band; n. primitive kidney; c.mes. coelomic mesoblast; 

 v. anal vesicle ; p. mesenchyme cells lying in blastocoel. (Modi- 

 fied from C. Shearer, Q. J. M. S. vol. LVI.) 



The Trochosphere, with modifications, occurs as 

 a free-swimming larval form in a large number of 

 Annelids, which are thus widely dispersed from the 

 parent at an early stage of existence. Now it is of 



