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 preéminently 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. Goés 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 1s 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 1t 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 
