Structure of RMzopod Shells. 303 



lation both with each other and with the formation of the 

 pylom. This is easily explained by the fact that all depend 

 upon the same physiological cause in the soft body secreting 

 the shell. All the peculiarities of the monaxon-pylomatic 

 type, including even the formation of the pylom, are to be 

 referred to a uniaxial differentiation of the sarcode-body, which 

 no longer emits its pseudopodia equally distributed on all 

 sides, but for the most part, or even exclusively (imperforate 

 forms), from one point, namely through the pylom ; next to 

 this principal effluent point the flow of sarcode is strongest 

 at the opposite pole, and, indeed, sometimes, as in the amphi- 

 stome Ehizopoda, it is equally strongly developed at both 

 poles. By this orientation of the soft body in the direction of 

 a primary axis its formative or secretory activity is no longer 

 equally great in all directions, but localized in a corresponding 

 manner, so that the two poles of the principal axis are distin- 

 guished in the way above indicated by radial appendages of 

 various kinds from the more indifferent equatorial parts of 

 the shell. 



In a very great number of cases it is proved by observa- 

 tion that a strengthened main flow of sarcode takes its course 

 through the pylom, quite apart from the imperforate Thalarao- 

 phora and Radiolaria, in which, from the very nature of the 

 case, the whole of the pseudopodia must pass through the 

 pylom as the only aperture present. We may therefore with- 

 out hesitation regard such an arrangement as a general rule, 

 without requiring direct proof for every pylomatic llhizopod 

 shell. From analogy, i. e. supported by the numerous 

 actually observed cases and the harmonious intimate relation of 

 the different parts of an organism which no one can very well 

 doubt, this assumption is justified. 



It might perhaps be objected, however, that the pyloms of 

 the Ehizopoda being traversed by a stronger flow of sarcode 

 does not prove that the latter is also the cause of the forma- 

 tion of the apertures ; on the contrary, the opposite causal 

 nexus might exist and the sarcode cords principally issue 

 there, because a more convenient course is offered to them. 

 In answer to this objection it will suffice to indicate simply 

 that the soft protoplasmic body is the original thing^ and the 

 hard structure a secondary secretion from it. The soft body 

 forms the shell for itself in accordance wnth its wants, instead 

 of arranging itself to suit the shell ; the apertures of the shell 

 of course serve for the passage of the pseudopodia outwards, 

 the small pores for single ones, the great pylom-aperture for 

 a larger number of pseudopodia. 



In a number of pylomatic Ehizopoda the development of 



