26 EHIZOPODA. 



the remains, not of Numrmdites proper, but rather 

 of a form which, though resembling it closely in 

 external appearance, is in internal structure very 

 dissimilar. For this form he has proposed the 

 name of Orbitoides. The same observer has also 

 given it as his opinion, that between the existing 

 Nonionina and the true fossil Numifnulites there 

 exists no important difference of structure. 



13. Size of Rhizopoda. — All the Amcehea 

 are microscopic, being seldom known to exceed 

 •02 of an inch in diameter. The Foraminifera are 

 somewhat larger, the linear dimensions of the 

 recent British species (for example) varying from 

 •005 to '050 of an inch. But among the tropical 

 and extinct forms of the group we meet with 

 many whose size is much more considerable ; 

 NuTiimidites being frequently at least three inches 

 in circumference, while specimens of Cyclocly- 

 peus have been met with which have been found to 

 reach 2*25 inches in diameter. 



14. Development of Rliizopoda. — Almost 

 nothing is kno\\Ti of the development of the Rhi- 

 zopoda. Difflugia and Actinophrys have been 

 observed to undergo multiplication by fission (i. e. 

 the separation of the body into two parts), and the 

 last-mentioned form also propagates itself by a 

 peculiar method which presents some slight ana- 

 logy to the " conjugating process " among the 

 lower Algse. In the body of Orbitolites Dr. Car- 

 penter has observed the sarcode to be " broken up 

 (as it were) into little spherules," and these he sup- 

 poses are probably " gemmules " destined for ex- 

 pulsion through the marginal pores. He has also 



