98 H. GILBEKTSON- 



The Amoeba appears under the microscope to be something like a 

 piece of jelly, and if watched for a short time is found to have the 

 power of slow movement ; in fact it is a gelatinous contractile body 

 capable of locomotion by expansions of the sarcode or fleshy matter 

 thrown out from any point of the body. These expansions in- 

 sensibly glide along the surface of glass like a drop of oil, and 

 the enclosed granules of the main body are seen to run into them ; 

 thus the whole mass moves from place to place. Should an Amoeba 

 come in contact with starch granules, naviculae, vegetable debris, 

 etc., the sarcode opens out at any part and absorbs such substances, 

 and probably, by some form of digestive process, nutrition may be 

 obtained from them. This species, known as Amoeba diffluens, 

 does not secrete any covering or solid tissue, but other forms of 

 E-hizopoda, or root-footed animalcules, secrete a lorica or case, 

 which may be frequently seen to be tinted orange, yellow, or brown. 

 These cases appear to consist of a material resembling parchment, 

 and have a pitcher-like form, sometimes globular, at other times 

 oblong or spiral, and either smooth or sculptured ; sometimes the 

 lorica is covered with grains of sand similar to that of the caddis. 



Advancing another step, we find vast numbers of calcareous 

 shells of beautiful forms, both recent and fossil, known as Forami- 

 nifera, or shells with numerous openings ; they are very various in 

 their forms, and are secreted by the same jelly-like substance as 

 the Amoebina are composed of. 



Chalk, with which we in this district are so well acquainted, is 

 found to consist chiefly of these f oraminif erous shells or their debris ; 

 and when I tell you that the Chalk formation immediately be- 

 neath us is about 500 feet thick, as was proved last year by the 

 New River Company in boring for water between Hertford and 

 'Ware,'^ and that it extends from the Isle of Wight to Flamborough 

 Head, with a maximum thickness of about 1500 feet, you may form 

 some slight conception of what we owe to this low form of animal 

 life. Moreover, by deep-sea soundings made for the purpose of 

 finding a bed for the Atlantic cable, and still more recently by the 

 Challenger expedition, it has been found that at the present time 

 vast deposits of these shells are being made in eveiy quarter of the 

 globe, so that it has been said that we are still, geologically speaking, 

 in the Cretaceous age. 



There is yet another class of shell formed by this jelly-like sar- 

 code, viz. the Polycystina. These shells are built up of silex or 

 flint, and, as in the case of the Foraminifera, they are very various 

 and very beautiful. Like the calcareous Foraminifera, they are 

 found in great abundance both recent and fossil ; the well-known 

 bed of Polycystina in the Barbadoes is an instance of them in their 

 fossil state, and recent specimens may be obtained from great depths 

 in most seas, from the Mediterranean to the Sea of Kamschatka. 



Thus we have this jelly-like substance, or sarcode, known as the 

 Amoebina, when it secretes no shell or case ; the Arcellina, when it 



* See ' Trans. Watford Nat. Hist. Soc.,' Vol. II, p. 245. 



