14 LO WER INVER TEliRA TES. 



interior, where it undergoes digestion and assimilation. If the prey be larger, several 

 rays may bend toward it and together secure and draw it down to the body. 



Actinophrys propagates by simple division and by the fusing together of two or 

 more specimens into a single mass, which then reproduces new forms by fission. The 

 conjugation of two individuals is quite a common occurrence, but the Hon. J. D. Cox 

 has observed as many as nine individuals joined in the process. The same observer 

 also describes another method of propagation in which the parent form passes into an 

 opalescent condition, after which it undergoes segmentation into a brood of young. 



A much larger heliozoon, greatly resembling Actinophrys, is Actinosphcerium. It 

 is especially distinguished from the former by the frothy layer of ectosarc which sur- 

 rounds the central sarcode, and by the complex structure of the pseudopodal rays 

 which, under high magnification, seem to have a hard axis-cyUnder, probably only a 

 core of denser protoplasm. 



Perhaps one of the most beautiful forms of this order is Clathridina, represented 

 in Fig. 10. While young the capsules are colorless and clear, but with age they be- 

 come yellow. The sarcode does not usually fill the lattice-capsule, but is collected in 

 a ball within it. It is a very beautiful species ; often found in great abundance in ponds 

 and ditches. 



The Heliozoa seem to be quite closely related to the Radiolaria, but the exact rela- 

 tions of the two gi-oups is not yet known. It has been suggested that the Heliozoa are 

 embryonic forms of the more highly-developed group ; but until the structure of both 

 groups is more fully elucidated it seems useless to speculate much about this question. 

 Several observers have noticed within Actinophrys a peculiar nuclear sphere which 

 greatly resembles the central vesicle of certain Radiolaria. 



Order IV. — RETICULARIA. 

 Sub-order I. — Protoplasta. 



This sub-order includes a considerable number of fresh-water Rhizopods with very 

 soft sarcode bodies and delicate, branching, thread-like pseudopodia. The endosarc 

 and ectosarc are even less clearly differentiated than in the lobose forms. The nucleus 

 is usually large, and several contractile vesicles are to be seen in the endosarc. 



A characteristic Rhizopod of this sub-order is Gromia oviformis, represented in 

 Fig. 11. The shell is thin, chitinous, colorless or yellowish, measuring about .115 mm. 

 in length. A high power of the microscope shows an incessant streaming of granules 

 along the branching, anastomosing shreds of sarcode, the granules moving outward on 

 one side and back on the other side of each filament. The sarcode extensions of Gromia 

 anastomose more freely than is usual among the Protoplasta Filosa, resembling more 

 closely the Foraminifera in this respect, and the contractile vesicle is near the mouth 

 of the shell. In fact. Prof. Joseph Leidy, in his monograph on the "Fresh-water 

 Rhizopods of North America," has placed Gromia among the Foraminifera. The 

 filose protoplasts seem to be in nowise different from the Foraminifera, except that 

 the shells of the latter are usually calcareous, and the pseudopodia manifest a greater 

 tendency to anastomose, and are more granular. 



The shells of the filose protoplasts are usually composed of a clear, chitinous sub- 



