370 THE AMERICAN MONTHLY FDec 



Each succeeding chamber extends a little beyond its pre- 

 decessor. This lapping of the chambers at the ends causes 

 the increase in the longitudinal dimensions of the shell 

 as it grows by the addition of chamber after chamber. 

 The size of the chambers and the thickness and strength 

 of their walls increase from the center out. An open pas- 

 sage bearing a resemblance to the siphuncie in cephalo- 

 pods lies as a trough along the ventral side of the cham- 

 bers and cuts away the lower half of the septa where it 

 passes through them. 



The name "involute sinus" has been proposed by Pro- 

 fessor Williston for this trough-like passage. The width 

 of the openings in the septa increases from about 1-25 

 mm. at the nucleus to 1 mm. in the outer whorls. The 

 septa are also punctured by many minute circular open- 

 ings (foramina) which were once occupied by the pseudo- 

 podia of the animal, and later served as ways for the pro- 

 toplasm of the animal to commuicate from chamber to 

 chamber. The outer walls of the chambers possesses very 

 few if any foramina or other openings. They are slight- 

 ly more convex than the general curve of the whorl, and 

 extend in graceful double curves from the girdle to either 

 end, giving a corrugated appearance to the outer surface 

 of the shell. The living Fasulina was evidently one com- 

 posite body, occupying all the chambers of the entire 

 shell at the same time, with a common vitality ; a contin- 

 ual circulation of protoplasm taking place from chamber 

 to chamber through the minute foramina and the siph- 

 uncle-like openings in the septa. The first chamber oc- 

 cupied by the young Fusulina is nearly spherical. A spher- 

 ical first chamber is found in a great number of Foram- 

 inifera whose later forms bear no resemblance to a sphere, 

 the form of the succeeding chambers and the final shape 

 of the adult shell depending upon the order in which the 

 multiplication of chambers takes place and their man- 

 ner of attachment to the parent mass. 



