RHIZOPODA. 7 



according to definite laws. The spaces of these chambers com- 

 municate by means of narrow passages and large openings in the 

 partition walls. In like manner those portions of the protoplasm 

 which are enclosed in the individual chambers are in direct commu- 

 nication with one another by means of processes which pass 

 through the passages and openings in the septa, and connect one 

 portion with another. In the perforated forms there may be an 

 additional complication owing to the formation of a secondary 

 shell by the protoplasm. This secondary shell is placed outside 

 the primary, and is traversed by canals containing the protoplasm. 

 The multinucleate condition is very generally found, and probably 

 constitutes a phase in the life-history. For instance, in Gromia 

 and Difflugia specimens have been found with a large number of 

 nuclei, though the usual condition appears to be with one nucleus. 

 The quality of the body-substance, the mode of movement and 

 nourishment, agree closely with those which have been depicted as 

 characteristic of the class. Our knowledge of the mode of repro- 

 duction is imperfect. Amongst the forms without a shell, fission 

 has been observed. In Haliphysema one of the nuclei with a small 

 portion of protoplasm is said to become marked off from the rest 

 and to form a small body not unlike an ovum imbedded in the 

 protoplasm. This may be called internal budding. 



In several of the families of our order (MilioUdce, Lagenidce, 

 Rotalidce, and Nummulinidce) we meet with the phenomenon of 

 dimorphism, that is to say, the species is made of two distinct kinds 

 of individuals, which appear to alternate with one another in the 

 life-history. (Fig. 5.) The one of these forms the microspheric is 

 distinguished by the small size of the initial chamber and by the 

 possession of a large number of small nuclei ; while the other the 

 megalospheric has a large initial chamber and one large nucleus. 

 In the microspheric form, reproduction is effected by the simple 

 emergence of the protoplasm from the shell and its division into a 

 number of spherical bodies; each of these secretes a shell which 

 constitutes the first chamber of a megalospheric form. In the 

 megalospheric form, on the other hand, the protoplasm in the 

 shell breaks up into a number of small masses, each of which 

 issues as a flagellated zoospore. The further history of these is not 

 known, but they probably give rise to the microspheric form. 



In Polystomclla crispa L., one of the Nummulinidce, whose life-history is better 

 known than that of other Foranrinifera, the initial chamber, or microsphere, 

 occupying the centre of the shells of the microspheric form, has a diameter 



