METAZOA VERMES. 283 



bers of this family, and the stages in the ontogeny of the 

 brachial supports of the specialized members ; such, for 

 instance, as Magellania. In Gwynia capsula Jeffreys 

 (PI. 699, A), one of the most primitive members of the 

 Terebratellidae, the brachial supports never undergo a 

 metamorphosis but remain essentially the same through- 

 out life. They consist of two descending branches or 

 lamellae which are not attached to the crura and which 

 do not unite to form a complete loop. The crura from 

 which the lamellae ultimately extend in most genera are 

 seen at the posterior end of the valve in all the figures. 



Cistella neapolitana Scacchi (PL 699, B), has a median 

 septum with a calcified loop attached which is united to 

 the crura. 



A small ring appears on the septum in Bouchardia rosea 

 Ma we (PI. 699, C, Ca, side view), which is the begin- 

 ning of the secondary loop. The parts become more 

 united in Megerliiia lamarckiana Davidson (D), while in 

 Magas pumilus Sow. (E), the descending branches are 

 completed, though the ascending have not united. Maga- 

 sella cumingi Dvds. (F), shows the character of the de- 

 scending and ascending loop more distinctly, which 

 reaches a still more specialized condition in Terebratella 

 rubicunda (G). Here we have the descending loop with 

 the septum and connecting band or jugum and the com- 

 pleted ascending loop. 



A further change takes place in Magellania flavescens 

 Lam. (PI. 699, H), in which the septum and connecting 

 bands seen in Terebratella have been resorbed. These 

 eight figures represent as many adults of eight different 

 genera, ranging from the most primitive to the most spe- 

 cialized of the Terebratellidae. 



When the life history of the last named genus, Magel- 

 lania, is studied, it is found that it epitomizes in its own 

 development the history of these genera, and in this way 

 the history of the family to which it belongs. 



The larval Magellania is without calcified brachial sup- 



