PROTOZOA. 41 



great depths of the sea. The figures of Haeckel l show 

 that this genus and several other genera of the Radiolaria 

 have remained essentially unchanged since protozoic 

 times. Some of the Radiolaria have spines, as seen in 

 PL 45, figs. 3-5. Fig. 3, Xiphosphoera, has two equal 

 spines; fig. 4, Staurosphoera, has four; while fig. 5^ 

 Acanthosphoera, has numerous spines at the nodes of the 

 lattice work, though only three have been preserved. 

 The basket form is seen in Tripodiscium (PI. 45, fig. 6) r 

 while in fig. 7 (which belongs to the section of the 

 Dicyrtida, though the family is not /determined) the shell 

 is divided into three parts with numerous spines. 



It has been pointed out by Haeckel that the simple 

 skeletonless Heliozoan, Actinophrys, might give rise to 

 the simple shell-less Radiolarian, Actissa princeps Hkl. 

 (PI. 46, fig. 2), the stem-form from which probably the 

 whole group of Radiolaria has descended. The young 

 Actissa (fig. i) possesses one nucleus and is a flagellate 

 form. This passes probably into the Actinophrys stage 

 which unfortunately has not been observed. Afterward 

 a membrane, known as the central capsule, forms, which 

 is wholly absent in the young. The possession of this 

 organ separates the adult and more specialized Actissa 

 from Actinophrys, and is the peculiar and marked charac- 

 teristic of a Radiolarian. PL 46, fig. 2, is the adult. 

 The large round nucleus is seen in the center with its 

 nucleolus. Around the nucleus is finely granulated pro- 

 toplasm containing many clear spherical vacuoles. These 

 parts are contained in the porous central capsule ; outside 

 of the capsule is seen the jelly envelope or calymma 

 which in the figure is yellow but colorless in the living 

 Radiolarian. It is indeed seldom visible in the living, 

 freshly taken animal when observed in sea water, but 

 since it does not readily become colored, its size and form 

 can be made out definitely by placing the specimen in, 



1 Challenger Report, Zool, XVIII. 



