42 TOILERS IN THE SEA. 



that these, at the time of their birth, are in a com- 

 paratively high state of development." l 



Reproduction by gemmation is as probable in the 

 Foraminifera as in Difflugia, in which latter it has 

 been observed. When these animals are obtained in 

 considerable numbers, the formation of colonies by 

 gemmation (or budding) may easily be watched. 

 This process takes place in the foot (pseudcpodittm), 

 which gradually increases in size, acquires a nucleus 

 and investing membrane, which ultimately separates 

 and becomes a free animal. 



The structure of the shells, in several different 

 species, was the subject of careful investigation by 

 Professor Williamson many years ago, and some 

 interesting facts were then first brought to 

 light. One of these series of facts serves to throw 

 some light on the habits of the little-known 

 animals which inhabit these shells. It was found 

 on cutting sections, that the oldest cells have the 

 thickest walls, and the youngest, or last-formed 

 cells or chambers, the thinnest, and between these 

 every gradation of thickness. This indicates succes- 

 sive depositions of calcareous matter on the exterior, 

 for, if in the interior, the cavities would have been 

 reduced and ultimately blocked up. The hypothesis 

 suggested is thus stated : " I have come to the con- 



1 "Ann. Nat. Hist.," vol. viii. (1861) p. 320. 



