122" DEVELOPMENT AND HEREDITY. 



celled animal may have several nuclei. Thus we see 

 that the nucleus affords no basis for the assumption 

 of such a profound distinction between the two 

 groups. The presence of cell walls seems, there- 

 fore, to be the one distinguishing characteristic 

 separating the metazoa from the protozoa. This 

 characteristic, however, loses much of its impor- 

 tance in view of certain conditions obtaining among 

 the protozoa. If we examine a Radiolarian, we find 

 that its protoplasm is not perfectly homogeneous ; 

 it possesses a skeleton, which is partly internal, and 

 this makes certain divisions in the protoplasm. Ac- 

 tinosphsera, which has no hard skeleton, has its 

 protoplasm divided by membranes, in the form of 

 concentric spheres, and intersecting radial planes, 

 thus forming a true cellular structure, except that 

 a nucleus is not present in every cellular space. I 

 have seen a green zoospore of CEdogonium being 

 digested in one of these cellular spaces of the Acti- 

 nosphasra, and observed, after the chlorophyl bodies 

 were broken down, and when the green mass of the 

 zoospore seemed completely dissolved in the proto- 

 plasm of the Actinosphasra, that the green colouring- 

 matter filled even into the corners of the cellular 

 space, but did not penetrate beyond the membrane 

 which limited it. We find here, among the Radiola- 

 rians, a plan of structure closely approaching that 



