their Relation to Geological Formations. 19!) 



sinking in it at will ; but there is nothing recorded to support 

 the idea that they are alive, except their occurring in the greatest 

 numbers on the surface after sunset ; from which it is inferred 

 that they avoid the light. The presumed fact is certainly sin- 

 gular if the creatures are dead, though it may not be beyond 

 a physical explanation. But if they are living, it is equally 

 singular that no manifestations of vital functions have been 

 observed, as far as I can ascertain, in any captured specimens, 

 by those who have had the opportunity of examining them. 

 Prof. Wyville Thomson and assistant Mr. Murray (who has 

 been paying the closest attention to the floating Foraminifera) 

 would scarcely be unmindful of this matter ; yet it is note- 

 worthy that they " never have been able to detect in any of 

 the large number of Glohigerinn' which have been examined " 

 by them " the least trace of pseudopodia, or any extension 

 in any form of the sarcode beyond the shell." Moreover 

 the chambers are often almost empty, even in the freshest- 

 looking specimens ; or they contain sarcode apparently in 

 no other than the unsatisfactory condition it presented to 

 Bailey, Ehrenberg, Wallich, and others. So far, then, I see 

 no reason to change the opinion which is expressed in my 

 Notices of 1862. 



In order to explain all the circumstances under which the 

 ooze-forming foraminifers occur, I am induced to make the 

 following suggestions in accordance with the assumption that 

 they live at the bottom. As soon as a Globigerine or an Orbu- 

 line dies, the decomposition of the sarcode generates within 

 the chambers sufficient carbonic-acid gas to cause it to rise to the 

 surface. Here, the sarcode being still in process of decomposi- 

 tion, gas continues to be discharged from the chambers alter- 

 nately with the intromission of Avater : these actions give rise 

 to variations in the specific gravity and, as.a consequence, to 

 opposite vertical movements of the shell. It is conceivable, 

 all other conditions being favourable, that occasionally, after 

 the superficial stratum of the ocean has got warmed by the 

 noon-day sun, the elevated temperature, and the consequent 

 acceleration of the decomposition of the sarcode, Avould largely 

 increase the generation of gas, thereby causing the shell to 

 rise to or near the surface towards or after snnset : during the 

 night, on the gas escaping and its replacement by water, the 

 shell would descend again *. Thus, as long as decomposition 



• It is stated by Lewy that the amount of oxygen in sea-water is 

 somewhat greater "dui-ing the day than it is at night, the reverse being 

 the ca.se as regards carbonic acid (Bischof, vol. i. p. llo). May not this 

 difference have something to do with the lising of the shells during the 

 night !- 



14* 



