20 ZOOLOGY FOR MEDICAL STUDENTS chap. 



foramina and through these the protoplasm is continued outwards to 

 form a thin laver of external protoplasm which enslieathes the whole shell. 

 The shell is therefore not an external shell like that of a snail l)ut an 

 internal skeleton completely emliedded in lining substance. The external 



protoplasm extends outwards — when the creature is acti\"e — into pseudo- 



Polystomelia, ali\'e. Certain of the; piL-udnpoOi.i tnwarcU the hiwer side of the hgure arc flowing 

 round a particle of food. 



podia (Fig. 7) which are howexer in appearance totall}- unlike those of 

 Amoeba. They are ver)- long slender threads of protoplasm which show 

 a marked tendency to fuse in places with their neighbours. With a 

 high magnification it may be seen that there is a constant slow circulation 

 in the extruded pseudopodium — the cytoplasm streaming outwards alono" 



