128 J. J. LISTER. 



2. 

 (a.) Polystomella crispa (Linn.). Figs. 1-3 and 5-32. 



In the hope of throwing light upon the life-history of 

 Foraminifera, I have examined a large number of specimens of 

 Polystomella cnspa (Linn ), a species of almost cosmopolitan 

 distribution in shallow water, and abundant in the pools of our 

 own shores. 



Methods. — In collecting material I have used a large horse- 

 hair sieve with bolting cloth fastened beneath it. The sieve is 

 set in a shallow pool, and handfuls of seaweed are torn from the 

 rocks and shaken in the water standing in the sieve. The 

 small creatures which live amongst the weed, including the 

 Foraminifera, fall through the meshes of the sieve and are caught 

 by the bolting cloth. 



I have tried several reagents for killing the specimens, and 

 have obtained fairly satisfactory results with warm saturated 

 solution of corrosive sublimate and glacial acetic acid, in pro- 

 portions about 4 to 1. The advantage of this reagent is that 

 the walls of the chambers of the peripheral whorl are rapidly 

 dissolved by the acid, so that it is not long before the proto- 

 plasm is killed. 



After thoroughly washing in water, the specimens were 

 stained for some hours in picro-carmine. By this means the 

 nuclei are stained bright red, and the protoplasm pale yellow. 



Many specimens have been examined by means of sections, 

 but the majority have been mounted whole. 



As has been shown to be the case in so many other Forami- 

 nifera, this species is dimorphic. Externally the two forms are, 

 so far as I am aware, undistinguishable ; but, on examining 

 decalcified and stained specimens, they may be at once referred 

 either to the megalospheric or microspheric fiarm. 



These differ from one another in respect of the size and 

 shape of the central chambers, and in respect of their nuclei. 



The megalospheric form (fig. 13) has a large central chamber, 



