PROTOZOA. 43 



a differentiation in the processes which have produced the 

 zoons. Fig. i is known as an isospore ; it is provided 

 with a whip, a homogeneous nucleus of uniform^ constitu- 

 tion, and a little rod-like crystal. Figs. 2 and 3 represent 

 the anisospores (fig. 2 the large macrospore and fig. 3 the 

 smaller microspore) which are never produced by the less 

 specialized Actissa. These are provided with a whip, 1 

 a heterogeneous nucleus of two-fold constitution, and fat 

 granules, but the crystal is often wanting. Unfortunately 

 all attempts have failed to follow the development of 

 the flagellate young to the typical Radiolarian condition 

 represented by Actissa. It is probable, however, that 

 the phenomenon of accidental fusion of different zoons 

 observable in the simpler Rhizopods has given rise in the 

 colonial Radiolaria to the phenomenon of genetic union 

 or conjugation, and that the macrospore and microspore 

 unite ; if this is true we may have here the simplest form 

 of sexual reproduction. After this possible union it is 

 probable that a single form arises like Actissa which 

 becomes a colony by the division of the nucleus, the prod- 

 ucts of the division remaining united as seen in fig. 4, 

 which is a young, unarticulated colony. Fig. 5 is a piece 

 of a young colony showing how the many central capsules 

 (represented by red dots in fig. 4) have arisen. There 

 are eight of these capsules, two of which are in the act of 

 dividing. The nucleus is seen in different stages of divi- 

 sion. Around the central capsules extends the jelly-like 

 calymma (blue in the figure) comparable with the jelly 

 envelopes (yellow in the figure) of Actissa. Numerous 

 vacuoles and yellow cells are seen in the calymma. The 

 latter contain starch and are unicellular yellow algae which 

 live with many Radiolaria. True to their plant nature, 

 these yellow cells give out oxygen which is eagerly taken 

 by the Radiolarian, while the latter, equally true to its ani- 



1 Brandt says they possess most probably two whips (see Fauna 

 und Flora des Golfes von Neapel, XIII, p. 167). 



