21 



In these low grades of animal life, the spores are nearly always at some 

 period of their life free ciliated bodies swimming about in the water, and carried 

 to and fro by currents. At that period of their development, when they assume 

 a fixed habit of life — as is the case with many of the corals and MedusiB — they 

 attach themselves to the most convenient body they may happen to come into 

 contact with, generally speaking a rock under water, and there they flourish, and 

 soon become a fresh colony. Of course it is necessary for the climatal conditions 

 to be such as are favourable to the animal before it can live in its new situation. 



Although the means of distribution of these lower animals are so perfect, yet, 

 nevertheless, the same general rule of peculiarity of distribution applies to them 

 as well as to the higher forms of Ufe, though in a far less degree. Thus we find 

 that a natural banier, such as an isthmus between two seas has the same effect 

 on the distribution of aquatic animals, as a strait has on land animals ; as an 

 example of this, none better, I believe, can be found than that of the Isthmus of 

 Suez, separating the Mediterranean Sea from the Red Sea. 



Although the conditions of life on both sides of this isthmus are much the 

 same, yet, according to Ehrenberg, out of 120 species of Anthozoa (corals, &c.), 

 there are only two species common to both seas. 



It should be remarked also that in these low classes, as in the higher, those 

 forms which have the greatest powers of locomotion, ana also those forms which, 

 from their inhabiting the depths of the ocean, can get a very uniform temperature 

 everywhere, are the most widely diffused. In support of the first of these state- 

 ments I may adduce the case of the Sertularidse, and of the Hydridse, and of the 

 class Infmsoria, all of which include animals of very perfect means of locomotion 

 and of almost universal distribution. In support of the second statement no 

 better example can be found than the Foraminif era. These animals, which are 

 little else besides living jelly, inhabiting however very beautifully formed shells, 

 live at the bottom of the sea, where the temperature is very much the same all 

 over the world, and hence they are not much affected by the obstacle of climate, 

 and accordingly they are found nearly everywhere ; one genus especially, namely, 

 Globigerina, being almost cosmopolitan. To the geologist they are a singularly 

 interesting group, as their calcareous shells go to form great mountain ranges called 

 Nummulitic Formations. 



These rocks are found of many thousand feet of thickness in the Alps and 

 the Carpathians, in Algeria and Morocco, also in Egjiyt, and as far as the frontiers 

 of China, showing that these animals had as extensive a range in geological 

 periods as at present. These Nummulitic- formations are usually referred to the 

 Middle-Eocene. 



There is good reason for thinking that a deposit of Foraminifera is going on at 

 at present in the North Atlantic. 



Passing on now to consider the means of distribution of the moUusca (i.e., 

 shellfish, &c.), we find that here also a somewhat similar device exists as among 

 the two lower sub-kingdoms ; for very frequently the young fry or larvae Are fur- 

 nished with cilia with which they can row themselves about. 



