1007.] The Foraminifera. 489 



WEEKLY EVENING MEETING, 

 Friday, February 15, 1907. 



His Grace the Duke of Northumberland, K.G. P.O. D.C.L. 

 F.R.S., President, in the Chair. 



Joseph Jackson Lister, Esq., M.A. F.R.S. 



The Foraminifera. 



The lecturer proposed to begin his discourse by describing the 

 mode of occurrence of the Foraminifera in nature and something of 

 their way of Hfe and their structure. He would then pass on to con- 

 sider certain problems which have arisen in the course of their study, 

 and trace the steps by which the solution of one of these problems has 

 been attained and, in the case of another, attempt to show the direc- 

 tion in which the solution appears to lie. 



The hollows between the ridges in a stretch of ripple-marked sand 

 are often found to be white with multitudes of shells of minute size 

 and exquisite shapes. If seaweed from shore pools or shallow water 

 is shaken in water over a sieve similar shells are found in the sand 

 which comes through. 



[A lantern slide of " floatings " from sand obtained in this manner 

 from Drake's Island, Plymouth Sound, was here shown.] 



Microscopically examined these shells are usually found to lie made 

 up of separate compartments or chambers, communicating by passages 

 and disposed in some regular plan — plani-spiral, helicoid, alternating 

 on either side of a straight axis, or some other plan. They differ too 

 in texture, being transparent and perforated by minute pores or porce- 

 lainous and imperforate. The shells are made of lime contained in 

 an organic basis of " chitin," and grains of sand may be included. 



The planispiral chambered shells were classified by the older 

 naturalists in the genus Nautilus among Cephalopod mollusca. These 

 were divided by d'Orbigny into SiiJhoniferes and Foraminiferes. 



In sand from littoral sea-weed many of the shells will be found to 

 contain the living animal. If slides are set on the sand overnight the 

 animal will crawl on them and they may then be taken out and 

 examined under the microscope ; the radiating pseudopodia will be 

 seen, attaching the animal to the substratum and its means of locomo- 

 tion. 



[A diagram of PolystomelJa cris2)a with extended pseudopodia was 

 here, exhibited.] 



The hyaline substance forming the pseudopodia is protoplasm. On 



