110 THE SEA SHORE 



it down till a very thin section is obtained. Such a section, when 

 viewed under the low power of a compound microscope, will be 

 seen to consist very largely of minute shells ; though, of course, the 

 shells themselves will be seen in section only. 



The extensive beds of numniulitic limestones found in various 

 parts of South Europe and North Africa are also composed largely 

 of foraminifer shells, the most conspicuous of which are those 

 already referred to as nurnmulites disc-shaped shells of a spiral 

 form, in which the older chambers overlap and hide those that 

 enclose the earlier portion of the colony. 



Before concluding our brief account of these interesting marine 

 protozoons, it may be well to point out that, although the forami- 

 nifera belong to the lowest class of the lowest sub-kingdom of 

 animals, yet there are some rhizopods the Monera, which are 

 even simpler in structure. These are mere specks of undif- 

 ferentiated protoplasm, not protected by any shell, and not even 

 possessing a nucleus, and are the simplest of all animal beings. 



The second division of the Protozoa the class Protoplasta 

 has already received a small share of attention, inasmuch as the 

 amoeba, which was briefly described as a type of the whole sub- 

 kingdom, belongs to it. 



The study of the amoeba is usually pursued by means of speci- 

 mens obtained from fresh-water pools, and reference has been 

 made to it in a former work dealing particularly with the life of 

 ponds and streams ; but it should be observed that the amoeba 

 inhabits salt water also, and will be frequently met with by those 

 who search for the microscopic life of the sea, especially when 

 the water examined has been taken from those sheltered nooks of 

 a rocky coast that are protected from the direct action of the 

 waves, or from the little pools that are so far from the reach of the 

 tides as to be only occasionally disturbed. Here the amoeba may 

 be seen creeping slowly over the slender green threads of the con- 

 fervae that surround the margin of the pool. 



The third class Radiolaria is of great interest to the student 

 of marine life, on account of the great beauty of the shells ; but, 

 as with the other members of this sub-kingdom, a compound micro- 

 scope is necessary for the study of them. 



The animals of this group resemble the foraminifers in that 

 they throw out fine thread-like pseudopods, but they are dis- 

 tinguished from them by the possession of a membranous capsule 

 in the centre of the body, surrounding the nucleus, and perforated 



