POLTCYSTIXA. 29 



nislied {fig. 5). The contained animal consists 

 of an olive brown sarcode substance capable of 

 protruding pseudopodia through the numerous 

 foramina with which the shell is perforated. In 

 those forms which have been most carefully exa- 

 mined, the sarcode body, which is divided into four 

 equal lobes, does not fill the entire cavity of the 

 shell, but would seem to be wholly confined to the 

 upper portion of the latter. Of the true nature of 

 these creatm-es, much has yet to be learned. 



2. IJisti-!!)'!i*i<i» s. — The Polycystina are very 

 widely distributed. Their shells, mingled with 

 those of Foraiiiinifera and Diatomacece, have been 

 ascertained to form part of the extensive organic 

 deposit which is now being formed over a portion 

 of the bed of the North Atlantic. They have been 

 found also in the Mediterranean and various other 

 parts of the existing ocean. They appear, how- 

 ever, to have been even more numerous at former 

 periods, their remains having been already de- 

 tected in both the secondary and tertiary forma- 

 tions. Nearly 300 apparently distinct forms of 

 these animals have been discovered by Ehrenberg, 

 in a tertiary deposit which occurs abundantly 

 throughout an extensive district of the island of 

 Barbadoes. 



