158 THREE CRUISES OF THE "BLAKE." 



rian earth of Barbados, there was a period when radiolarian ooze 

 must have been an important deposit of the West Indian region, 

 probably during the time when the Caribbean was connected 

 with the Pacific. 



The arenaceous types of foraminifera, on the contrary, abound 

 in the bottom deposits of the Caribbean and Mexican districts, 

 and along the Western Atlantic, and the principal families are 

 all well represented in the " Blake " collections. On some bot- 

 toms, the rhizopods vie in the variety of their development with 

 those found in some of the celebrated tertiary and cretaceous 

 localities. 



There is a marked absence of siliceous sand and a scarcity of 

 siliceous spicules from the coralline and calcareous ooze, so that 

 rhizopodan types are preeminently calcareous ; only a few suc- 

 ceed in making up their tests entirely of siliceous particles. We 

 shall therefore find associated siliceous and calcareous forms 

 greatly differing in outward shape, but Dr. Goes is inclined to 

 consider this as of small importance, and due entirely to the 

 difference of materials employed by one and the same type, 

 according to the character of the bottom, and that a sort of 

 isomorphism is established between species formerly considered 

 as belonging to either the arenaceous or vitreous groups. 



Where there are such enormous changes going on during the 

 growth of a species, it is natural that in this group, as well as 

 in sponges, we should find it extremely difficult to retain our old 

 notions of species ; and until the careful investigations of Wil- 

 liamson, Parker, Carpenter, and Brady among the foraminifera, 

 and of Haeckel among the sponges, but little systematic order 

 had been established in these groups. Endless generic and 

 specific names followed in rapid succession, till the task of iden- 

 tifying any form of these groups seemed hopeless. 



While among the more highly organized invertebrates the 

 effect of the nature of the bottom is seen rather in an association 

 of animals characteristic of rocky, gravelly, muddy, or sandy dis- 

 tricts, we find that in such groups as the sponges and rhizopods 

 the nature of the bottom is an all-essential factor in modifying 

 the organism. 



The bottom of the slopes and plateaux, and of the area where 



